Volume 1

Gene expression / Benjamin Lewin.

  • Lewin, Benjamin.
Date:
1974-1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression / Benjamin Lewin. Source: Wellcome Collection.

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    nucleic acid biochemistry. Because a solely conceptual account of molecular biology would tend to present too absolute a picture, I have endeavoured to point out the limitations of the experiments upon which our ideas rely; it is easy to state conclusions but important to realise the intricate, sometimes fragile, chain of deductions upon which they rest. I have tried to draw a broad picture of the processes involved in gene expres sion which will be useful both to students and to those engaged in research in these and related topics. I have in general presented this material in a logical rather than historical sequence; this means that experiments are discussed in an order which may sometimes differ from that in which they were performed. I have also attempted to convey the sense of intellectual excitement which provided the impetus for this research; to this end I have tried to indicate briefly our state of knowledge when critical experiments were performed and have on occasion digressed into a historical exposition. Molecular biology continues to generate enthusiasm, of course, and I have not confined this account to a description of what seems to have been established ; I think it is equally important to communicate the problems with which we are now concerned and to include some of the speculations presently occupying molecular biologists. This book starts with a discussion of the genetic code, which must surely be central to any account of gene expression. The details of how protein chains are elongated, initiated and terminated occupy the next two chapters. Our ideas on these topics are similar to, although naturally somewhat more developed than, the account which I presented four years ago. A notable advance, however, can be seen in the research described in the next chapter, which discusses the structure, function and biosynthesis of the ribosome. We can see here the promise that in time the position and role of each com ponent of the bacterial ribosome will be fully defined. The last chapter of this section of the book describes the general conclusions which we can formulate about the functions of transfer RNA; although many more tRNAs have now been sequenced, no rules relating structure to function have yet been discovered and our best hopes for further progress must lie with the characterization of more mutant tRNAs. A considerable advance in our knowledge is reviewed in the next four chapters, which discuss the transcription of RNA and its control. An inevitable source of disappointment in any such account must be that we still know so little of the enzymic processes implicated in the synthesis of RNA. However, we have a much better idea of the extent to which the activity of RNA poly merase itself may be controlled in bacterial cells and during phage infection; and our knowledge of the control systems which act on bacterial opérons is greatly extended. Even the simplest model, the lactose operon, is subject to at least two control systems, one positive and one negative; and a yet more complex network of interactions takes place in other bacterial opérons and