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The RNA World

by Sidney Altman
1989 Nobel Laureate in Chemistry

 

The phrase "The RNA World" was coined by Walter Gilbert in 1986 in a commentary on the then recent observations of the catalytic properties of various RNAs. The RNA World referred to an hypothetical stage in the origin of life on Earth. During this stage, proteins were not yet engaged in biochemical reactions and RNA carried out both the information storage task of genetic information and the full range of catalytic roles necessary in a very primitive self-replicating system. Gilbert pointed out that neither DNA nor protein were required in such a primitive system if RNA could perform as a catalyst. At that time, it had only been demonstrated that RNA could cleave or ligate phosphodiester bonds. Nevertheless, as is a frequent occurrence in science, a general hypothesis was constructed from a few specific instances of a phenomenon. This hypothesis proved to be very effective in stimulating thought about the origin of life on Earth. Ensuing discoveries of other natural catalytic RNAs that could cleave and ligate phosphodiester bonds, and the very recent observation that the region surrounding the peptidyl transferase center of a bacterial 50S ribosomal subunit contains RNA and no protein, further buttress the hypothesis. Finally, the so-called "evolution in vitro" methodology, which is able to scan an enormous number of nucleic acid sequences in vitro for any given function, has revealed that RNA, indeed, can have many different catalytic functions as so can, presumably, DNA.

On further reflection, many doubts have been raised about whether or not the original genetic/catalytic material could have been RNA as we know it today because extreme conditions on the primitive Earth might have led to the rapid chemical degradation of RNA. Nevertheless, even if the precise chemical nature of the early genetic/catalytic material differed from present-day RNA, it seems reasonable to conclude that the RNA World did exist at some time. If very primitive life on Earth did not arise until about 3.5

billion years ago, there was, perhaps, a period of 0.5 billion years in which to sample many polymer sequences that originally arose through non-biochemical mechanisms and that ultimately evolved directed the first self-replicating systems.

My involvement in the discovery of the first catalytic RNA began in innocence during a study of tRNA biosynthesis in Escherichia coli. I was fortunate enough to isolate and characterize a precursor tRNA, one of the intermediates in the metabolic pathway leading to the synthesis of mature tRNA. As in all biochemical pathways, if one has an intermediate compound, there must be an intra-cellular enzyme that acts on this intermediate to take it to the next step in the pathway. This enzyme, ribonuclease P (RNase P), was readily identifiable. Its function was to cleave a phosphodiester bond at the start of the mature tRNA nucleotide sequence, thereby releasing the upstream extra or "precursor" nucleotides.

The total purification of RNase P proved to be a very difficult task. However, a perceptive and hard-working graduate student, Ben Stark, noticed that an RNA copurified with the protein in the enzyme preparation. He then devised a test to see if the RNA molecule was essential for the function of the enzyme. This test used the same strategy that Avery, MacLeod and McCarty had used to prove that DNA was the essential ingredient in bacterial transformation. In Stark's experiment, the test showed that the RNA was essential for RNase P function. This result explained why the purification, which had been designed to isolate a proteinaceous complex, was so difficult. It also led to much disbelief in the community of enzymologists.

We soon suggested that the RNA subunit of RNase P was part of the active center of the enzyme, by analogy to the then current picture of the ribosome. A few years later, however, Cecilia Guerrier-Takada, a postdoctoral fellow, demonstrated that this RNA, itself, was a true enzyme in vitro. At that time, Tom Cech had recently and independently observed phosphoester bond cleavage and ligation by a different RNA molecule. Cech's observation and ours, while still greeted skeptically by some members of the enzymological community, were soon universally accepted and within a few years other catalytic RNAs derived from plant pathogens and the human delta RNA were also found.

The chemical details of catalysis by RNase P remain to be fully worked out although a rough picture of this reaction is now available. A fascinating aspect of the RNase P "problem" is the vast difference in chemical make-up of subunits and catalytic mechanism of this enzyme as it is found in eukaryotes (e.g., the RNA subunit is not active in vitro) compared to these properties in prokaryotes. Evolution has presented us with contemporary versions of this enzyme that undoubtedly will someday tell us an interesting story of its progression from an RNA to various complexes of RNA and protein.

 

References:

Orgel, L. E., The origin of life on the Earth. Scientific American, October 1994, Volume 271, pages 76-83.

Orgel, L. E., The origin of life - a review of facts and speculations, Trends in Biochemical Sciences, December 1998, Volume 2-3, pages 491-495

http://www.nobel.se/chemistry/articles/altman/index.html

Hydrocarbons for the 21st Century - The work of the Loker Hydrocarbon Research Institute

by George A. Olah
1994 Nobel Laureate in Chemistry

 

Hydrocarbons derived from petroleum, natural gas, or coal are essential in many ways to modern life and its quality. The bulk of the world’s hydrocarbons is used for fuels, electrical power generation, and heating. The chemical, petrochemical, plastics and rubber industries are also dependent upon hydrocarbons as raw materials for their products. Indeed, most industrially significant synthetic chemicals are derived from petroleum sources. The overall oil use of the world now exceeds ten million metric tons a day. Ever increasing world population (about 6 billion to increase to 10 billion in a few decades) and energy consumption and finite non-renewable fossil fuel resources, which are going to be increasingly depleted, are clearly on a collision course. New solutions will be needed for the 21st century if we are to maintain the standard of living the industrialized world has gotten used to and the developing world is striving to achieve.

Recognizing the need for a long-range program of basic research and graduate education in the field of hydrocarbon chemistry, the University of Southern California established its "Loker Hydrocarbon Research Institute" in 1977. Generous donations from Donald and Katherine Loker, as well as other friends and supporters helped build an outstanding facility and program.

Hydrocarbon Chemistry

Hydrocarbons, the principal compounds of oil and natural gas, have to be chemically altered to make useful products and materials. This is carried out by chemical and petrochemical industries in processes such as isomerization, alkylation homologation, etc. These processes are frequently catalyzed by acids and involve electron deficient intermediates called carbocations. The Loker Institute has pioneered new methods to study such processes and their mechanisms. Research is also aimed at more efficient utilization of fossil fuel resources including recycling of carbon dioxide (a greenhouse gas) to useful materials. Studies are also directed towards developing new synthetic methodologies for chemical bond making and bond breaking processes. Polymeric materials derived from simple hydrocarbon precursors are the basis for new materials with exceptional electrical, optical, and magnetic properties. These materials find applications in information technology, photochemical energy conversion and biomedical devices.

Carbocarbons and their Chemistry

In studying hydrocarbons and their conversions, a wide variety of highly acidic systems called superacids have been developed. When higher valent Lewis acid fluorides such as SbF5 and TaF5 are combined with Brönsted acids such as HF or FSO3H, acids many billions of times stronger than sulfuric acid are obtained. In such superacidic media the lifetime of carbocations are sufficiently long to be examined by a variety of chemical and physical methods including nuclear magnetic resonance spectrometry.

Tertiary Butyl Cation
©Loker Hydrocarbon Research Institute

Acid catalyzed conversion of hydrocarbons such as cracking, isomerization, alkylation, oligo- and poly-condensation, etc. are of substantial importance. The fundamental chemistry of such hydrocarbon conversions involves carbocations and their reactions. Novel environmentally benign acid systems, including solid acids, are developed to overcome difficulties connected with toxic acids such as hydrofluoric or sulfuric acid. Isomerization and alkylation of saturated hydrocarbons to provide high octane gasoline are of particularly great importance in the petroleum industry. The Loker Institute has developed an environmentally friendly and practical alkylation process for the manufacture of high octane gasoline by using a modified hydrogen fluoride catalyst system of greatly reduced volatility and toxicity.

 

Dr. Olah preparing t-Butyl Cation.
Photo by Dr. Herwig Buchholz

In addition, the use of superacidic catalysts allow new ways to hydro-treat coals, shale oil, tar sands and other heavy petroleum sources and residues, and yield liquid hydrocarbons. New and environmentally safe gasoline and diesel fuel additives were also developed, resulting in higher octane gasoline and higher octane diesel fuels. These additives have also resulted in cleaner burning fuels and opened the way to exclude currently used other toxic additives.

Conversion of Methane or Carbon Dioxide to Hydrocarbons

The direct conversion of methane (i.e. natural gas) to higher hydrocarbons and derived products offers a viable alternative to Fischer-Tropsch chemistry (utilizing synthesis gas, i.e. CO and H2). Until recently, the utilization of methane as a chemical building block was limited to free radical reactions (combustion, nitration, chlorination, etc.). Various stoichiometric organometallic insertion reactions were also discovered, but their use is so far not practical. Superacid catalysts developed at the Institute permit oxidative condensation of methane to higher hydrocarbons, as well as the selective electrophilic conversion of methane to its mono-substituted derivatives such as methyl halides and methyl alcohol. Monosubstituted methanes can be further condensed to ethylene, propylene and derived hydrocarbons over zeolites or bifunctional acidic-basic catalysts, giving access to a whole range of hydrocarbons essential to our everyday life.

 

Methonium ion
©Loker Hyrdocarbon Research Institute

Mechanistic aspects of the methane conversion chemistry, particularly the role of pentacoordinate CH5+-type carbocationic intermediates, were also studied. Kekule’s conclusion dating back to the 1860’s that carbon cannot bound to more than four atoms of groups, i.e. it cannot exceed tetravalency, was refuted by discoveries obtained at the Institute. Dr. Olah’s substantial body of work in this area resulted in the realization that in electrodeficient (carbocationic) systems carbon can coordinate with five, six or even seven atoms or groups simultaneously and laid the foundation to what is now recognized as hypercarbon chemistry.

When hydrocarbons are burned they form carbon dioxide and water. They are thus non-renewable on the human time scale. Excessive burning of fossil fuels leads to increased atmospheric levels of carbon dioxide, which has been linked to global warming and climatic changes. In addition to trying to keep carbon dioxide levels down through reducing burning of fossil fuels (the basis of the 1997 Kyoto agreement), new solutions are needed. An innovative new approach pursued by the Institute is directed at reversing the process by producing hydrocarbons from carbon dioxide and water via methyl alcohol. Some of the underlying chemistry to convert carbon dioxide using hydrogen gas (obtained by electrolytically splitting water) is known. Metal or superacid catalyzed reduction pursued by the Institute has made significant progress to bring about the feasibility of CO2 conversion to methanol. However, electricity needed for generating hydrogen is costly and remains the key to practical applications. As we still cannot store electricity efficiently, power plants in their off-peak periods could produce hydrogen as a means of storing electricity. Hydrogen then could be used to recycle CO2 (from smokestack emissions or other concentrated sources, eventually even the atmosphere) into methyl alcohol and derived fuels. The carbon dioxide recycling technology now under development allows us not only to produce useful fuels and hydrocarbon products, at the same time can contribute to mitigating CO2 related global warming.


Diagram by Dr. G. K. Surya Prakash

Methyl alcohol and derived fuels can also be used to produce electricity in the new direct oxidation liquid feed fuel cells developed jointly by the Loker Institute and Caltech-JPL. When operating the fuel cell in its "reversed mode", carbon dioxide and water can be electro-catalytically reduced to methyl alcohol. While the recycling of carbon dioxide into hydrocarbons is a highly energy demanding process some applications, i.e. solar power related applications, may not be overly concerned with this high energy input requirement.

Even if technologies to generate energy from alternate sources are further developed (i.e. atomic, solar, wind, etc.), a concentrated research effort is required to find long-range solutions for future hydrocarbon needs. The effort must include the development of alternative hydrocarbon sources, a search for new chemistry directed towards exploitation of renewable fuels, as well as the development of more efficient and environmentally acceptable ways of utilizing and recycling our present resources.

The final solution to the shortage of hydrocarbons will come only when mankind can produce cheap energy through safer atomic energy (or even fusion) and other alternate sources. With abundant cheap energy, hydrocarbons will be produced from carbon dioxide of the atmosphere and water. In the meantime, however, it is essential that solutions be found that are feasible within the framework of our existing technological base.

http://www.nobel.se/chemistry/articles/olah/index.html

Asilomar and Recombinant DNA

by Paul Berg
1980 Nobel Laureate in Chemistry

 

dna-rna

Introduction

Advances in the life sciences, particularly in biomedicine, are increasingly being scrutinized and their acceptance questioned. Novel technologies and ideas that impinge on human biology and their perceived impact on human values have renewed strains in the relationship between science and society. Thirty years ago, nations were engaged in debates about whether recombinant DNA research, also referred to as gene splicing and genetic engineering, was too dangerous to be allowed to continue. Fears of creating new kinds of plagues or of altering human evolution or of irreversibly altering the environment were only some of the concerns that were rampant. Lingering doubts and concerns still persist about the use of that technology in the development of genetically modified plants and animals used as food. Notably, some nations have enacted legislation that prohibits genetically-modified plants and animals from entering into their food supply. Paradoxically, no such embargo exists for the drugs and therapies that have revolutionized the treatment of serious diseases although many of them were created with the same technologies.

Today, it is research with human embryonic stem cells and attempts to prepare cloned stem cells for research and medical therapies that are being disavowed as being ethically unacceptable. As with the genetically modified food controversy and other cases where science and public policy clash, there are repeated calls to convene an "Asilomar Conference" to examine and resolve the policy controversies.

 

Unique Conference

The lofty status of the Asilomar Conference and the deliberative process it spawned stems from its success in identifying, evaluating and ultimately mitigating the perceived risks of recombinant DNA. Looking back now, this unique conference marked the beginning of an exceptional era for science and for the public discussion of science policy. Its success permitted the then contentious technology of recombinant DNA to emerge and flourish. Now the use of the recombinant DNA technology dominates research in biology. It has altered both the way questions are formulated and the way solutions are sought. The isolation of genes from any organism on our planet, alive or dead, is now routine. Furthermore, the construction of new variants of genes, chromosomes and viruses is standard practice in research laboratories as is the introduction of genes into microbes, plants and experimental animals. Without the tools of recombinant DNA there would be no human or any other genome sequence. Equally profound is the influence it has had in many related fields. Even a brief look at journals in such diverse fields as chemistry, evolutionary biology, paleontology, anthropology, linguistics, psychology, medicine, plant science, and, surprisingly, forensics, information theory and computer science shows the pervasive influence of this new paradigm.

Additional testimony to the conference's success are the frequent calls to resurrect the "Asilomar Process" to resolve the ethical dilemmas posed by newly emerging ideas and technologies, most recently human embryonic stem cell research. Whether the Asilomar Conference model can duplicate its achievement for current conflicts is problematic. But in acknowledging its thirtieth anniversary, it is worth examining the circumstances that gave birth to the conference and how the outcome permitted the then contentious recombinant DNA technology to emerge and flourish.

Time and faulty memory have obscured some of the circumstances and events that led to the scientific breakthrough and the path to Asilomar. The emergence of a new paradigm in any field of science generates, along with the excitement of a new frontier and perspective, an uncertainty about its full implications. This was especially true for the geneticists that fueled the emergence of the recombinant DNA technology during the 1970s.

group photo-participants
(Left to right) Maxine Singer, Norton Zinder, Sydney Brenner, and Paul Berg were among the participants at the Asilomar Conference.
Copyright © National Academy of Sciences

 

Voluntary Moratorium

The concerns about recombinant DNA had their antecedent in the creation of a DNA molecule containing the entire Simian Virus 40 genome joined to a segment of DNA containing three genes responsible for galactose metabolism in Escherichia coli.1 But improvements in the technology, most notably the ability to clone DNA segments from virtually any organism on our planet,2 triggered a new level of concern which culminated in mid-1974 with a call for a voluntary moratorium on certain recombinant DNA experiments.3 This unprecedented action by a group of American scientists echoed reservations expressed at a conference on nucleic acids during the previous summer.4 Both groups acknowledged that the new technology created extraordinary novel avenues for genetics and could ultimately provide exceptional opportunities for medicine, agriculture and industry. Nevertheless, there were concerns that unfettered pursuit of this research might engender unforeseen and damaging consequences for human health and the Earth's ecosystems. In spite of widespread consternation among many scientists about the proscriptions, the validity of the concerns, and the manner in which they were announced, the moratorium was universally observed. One goal of the moratorium was to provide time for a conference that would evaluate the state of the new technology and the risks, if any, associated with it.

That conference, held at the Asilomar Conference Center on California's Monterey peninsula in the USA, included scientists from throughout the world, lawyers, members of the press and government officials.5,6 One aim of the meeting was to consider whether to lift the voluntary moratorium and, if so, under what conditions the research could proceed safely. Although there were few data on which to base a scientifically defensible judgment the conference concluded, not without outspoken opposition from some of its more notable participants, that recombinant DNA research should proceed but under strict guidelines.7 Such guidelines were subsequently promulgated by the National Institutes of Health8 and by comparable bodies in other countries.9,10

The primary motivation for the prompt actions taken by scientists and governments in the period 1973-1976 was to protect laboratory personnel, the general public, and the environment from any hazards that might be directly generated by the experiments. In particular, there were speculations that normally innocuous microbes could be changed into human pathogens by introducing genes that rendered them resistant to then available antibiotics, or enabled them to produce dangerous toxins, or transformed them into cancer causing agents. The uncertainties stimulated occasionally turbulent debates. Public fear was fanned by the popularity of visions of "The Andromeda Strain" and the myriad of 'what ifs' floated by both serious and demagogic commentators. Some scientists, and public officials as well, were certain that recombinant DNA research was flirting with disaster and that lifting the moratorium was a blunder. Others, reflecting their intuition and expertise, argued that such cells, viruses and recombinant DNAs posed no risk at all. The overwhelming assessment today is that the latter view was correct. Literally hundreds of millions of experiments, many inconceivable in 1975, have been carried out in the last 30 years without incident. No documented hazard to public health has been attributable to the applications of recombinant DNA technology. Moreover, the concern of some that moving DNA among species would breach customary breeding barriers and have profound effects on natural evolutionary processes has substantially disappeared as the science revealed that such exchanges occur in nature.

Watson and Brenner
(Left to right) James Watson and Sydney Brenner confer with each other.
Copyright © National Academy of Sciences

 

Recombinant DNA Technology

At the time of Asilomar, scientists optimistically predicted that the recombinant DNA methods would soon yield important drugs, industrial products and improved agricultural varieties. In fact, such developments took longer than anticipated. Some have never been realized because learning how to manipulate genes for useful purposes presented unexpected difficulties. Since the mid-1980s, however, the number of products has increased continually. Hormones, vaccines, therapeutic agents and diagnostic tools are enhancing medical practice. The production and consumption of genetically engineered food plants are realities although their dissemination has been limited. A thriving biotechnology industry has created products, interesting jobs and wealth for scientists and others. In retrospect, very few of those attending the Asilomar Conference foresaw the pervasive, complex, robust, and rich ramifications of recombinant DNA technology. Nor could most have predicted the pace at which fundamental understanding of biology has deepened.

Frequently heard in the 1970s were criticisms of scientists for assuming leadership in formulating policies that were matters of public concern. This led some scientists to believe that the public debate itself was a great threat and that the fallout of claim and counterclaim would bring debilitating restrictions or even prohibitions on molecular biological research. In truth, many scientists grew impatient with the time-consuming, contentious debates. Yet the effort to inform the public also encouraged responsible public discussion that succeeded in developing a consensus for the measured approach that many scientists supported. Restrictive national legislation was avoided, and in the long run, scientists benefited from their forthrightness and prudent actions in the face of uncertainty.

 

Ethical and Legal Implications

An often-voiced criticism of the Asilomar Conference discussions was the failure to consider the ethical and legal implications of genetic engineering of plants, animals and humans. Did the organizers and participants of the Asilomar conference deliberately limit the scope of the concerns? The participants were scored for ignoring the increased perils of biological warfare made possible by the development of the new recombinant technology. Others have been critical of the conference because it did not confront the potential misuse of the recombinant DNA technology or the ethical dilemmas that would arise from applying the technology to genetic screening and somatic and germ line gene therapy, or the environmental consequences arising from the creation of genetically modified food plants.10 It should not be forgotten that these possibilities were still far in the future and the more immediate issue confronting the Asilomar organizers and participants was the one the scientists had raised: the potential risks to human health and the environment posed by the expanding recombinant DNA technology. We could not avoid the question of whether there were serious health hazards associated with going forward with the experiments that were being planned. In short, the agenda for the three-day meeting had to focus on an assessment of the risks and how to eliminate or reduce the risks that seemed plausible. We accepted that the other issues would be dealt with as they became imminent and estimable.

(Left to right) Michael Bishop and Norton Zinder exchange views.
Copyright © National Academy of Sciences

 

Public Trust

What did the actions taken by the scientific community achieve? First and foremost, we gained the public's trust, for it was the very scientists who were most involved in the work and had every incentive to be left free to pursue their dream that called attention to the risks inherent in the experiments they were doing. Aside from unprecedented nature of that action, the scientists' call for a temporary halt to the experiments that most concerned them and the assumption of responsibility for assessing and dealing with those risks was widely acclaimed as laudable ethical behavior. If the Asilomar exercise was a success, it was because scientists took the initiative in raising the issue rather than having it raised against them; that initiative engendered considerable credibility instead of cynical suspicion of what was to follow. The public's trust was undeniably increased by the fact that more than 10% of the participants were from the news media. They were free to describe, comment on and criticize the discussions and conclusions at the end of the conference. All the deliberations, bickering, bitter accusations, wavering views and the arrival at a consensus were widely chronicled by the reporters that attended and subsequently by the rest of the media and subsequent commentators.5,9,10

 

Moving Science Forward

Is "the Asilomar model" appropriate for resolving or contributing to some of the "hot button" issues confronting scientists and the public today? For example, are the deep divisions about fetal tissue and embryonic stem cell research, somatic and germ-line gene therapy and directed genetic modification of food crops amenable to deliberation and resolution? I believe the Asilomar model would not succeed in dealing with those issues today to the extent it did 30 years ago with recombinant DNA for the following reasons. First, the public's awareness of the recombinant DNA breakthrough was sudden and unanticipated. It was more than just another interesting scientific advance because it brought with it potential dangers to public health. Furthermore, the implications of risk came from the scientists conducting that research, not from some investigative reporter or disaffected scientist; that was most unusual, even historic. There seemed to be an urgent need for consensus on how to proceed and a plausible plan on how to deal with issues, both of which were provided by the scientific community. Action was prompt and seen by the public to have been achieved by transparent deliberations and with considerable cost to their own scientific interests. The issue and its resolution were complete before an entrenched, intransigent and chronic opposition developed. Attempts to prohibit the research or reverse the actions recommended by the conference threatened but never generated sufficient traction to succeed.

By contrast, the issues that challenge us today are qualitatively different. They are often beset with economic self-interest and increasingly by nearly irreconcilable ethical and religious conflicts and challenges to deeply held social values. An Asilomar type conference trying to contend with such contentious views is, I believe, doomed to acrimony and policy stagnation, neither of which advances the cause of finding a solution. There are many forums for airing opposing views but emerging with an agreed upon solution from such an exercise is elusive and discouraging.

The Asilomar decisions emerged from a consensus of opposing views. Although the recommendations were clearly "inconvenient", the participants had a stake in having the science move forward and not in leaving the rules for conducting the research to be set by others. By contrast, there is little prospect for consensus in our society on the ethical issues concerning fetal tissue and embryonic stem cell research, genetic testing, somatic and germ-line gene therapy, and engineered plant and animal species and hence little incentive to seek a compromise. Compromise in those instances may only be achievable by political means, where majority rule prevails.

(Left to right) Joseph Sambrook and David Baltimore caught up in a discussion.
Copyright © National Academy of Sciences

 

Bibliography

1 Jackson, D.A., Symons, R.H. and Berg, P., "Biochemical method for inserting new genetic information into DNA of Simian Virus 40: circular SV40 DNA containing lambda phage genes and the galactose operon of Escherichia coli," Proc. Nat. Acad. Sci. USA 69, pp. 2904-2909 (1972).

2 Mertz, J.E. and Davis, R.W., "Cleavage of DNA by R1 restriction endonuclease generates cohesive ends," Proc. Nat. Acad. Sci. USA 69, pp. 3370-3374 (1972).

3 Berg, P., Baltimore, D., Boyer, H.W., Cohen, S.N., Davis, R.W., Hogness, D.S., Nathans, D., Roblin, R., Watson, J.D., Weissman, S. and Zinder, N.D., "Biohazards of Recombinant DNA," Science 185, p. 3034, also Science 185, p. 303 (1974).

4 Singer, M.F. and Soll, D., "Guidelines for hybrid DNA molecules," Science 181, p. 1114 (1973).

5 Rogers, M., "Biohazard," Alfred A. Knopf, New York (1977).

6 Fredrickson, D.S., "Asilomar and recombinant DNA: the end of the beginning" in Biomedical Politics, National Academy Press, Washington, D.C., pp. 258-292 (1991).

7 Berg, P., Baltimore, D., Brenner, S., Roblin, R.O. III, Singer, M.F., "Summary statement of the Asilomar Conference on recombinant DNA molecules," Proc. Nat. Acad. Sci. USA 72, pp. 1981-1984 (1975), also Science 188, p. 991 (1975).

8 "Guidelines for research involving recombinant DNA molecules," Federal Register 41, no. 131, pp. 27911-27943 (1976).

9 Fredrickson, D.S., Chapters 1 and 5 in "The recombinant DNA controversy. A memoir," ASM Press, Washington, D.C., p. 388 (2001).

10 Wright, S., "Molecular Politics: Developing American and British regulatory policy for genetic engineering," U. Chicago Press, p. 592 (1994).

http://www.nobel.se/chemistry/articles/berg/index.html

 





KNOWLEDGE FOR EVERYTHING