TIG -February 1987. Vol. 3, No. 2

primordial genes gave rise to more advanced genes with more sophisticated, similar functions but the homology was lost during evolution (divergent evolu- tion); or different primordial genes gave rise to today’s enzymes, which may share the same function only due to a fortuitous similarity in conformation (convergent evolution).

Since, as mentioned above, the amino acid and the nucleotide analysis have not always pointed to a common ancestor for proteins of similar function, the question remains open In such cases, is it too much to think that the ancestor of an enzyme found in higher organisms was performing a task different fiorn the one it is performing today, and that possibly in the evolution of the prokaryotes it took a different path so that the products of the same ancestor gene will be found

doing something entirely different in Werent organisms?

Another point raised in the book, but not conclusively resolved, is the roie (ii any) that introns played in tbe creation of multidomain protein genes, a subject most imaginatively discussed in the amusing Chapter 5.

Having read the book 1 am left with two stimulating core problems: (1) are the proteinsasweknowthemtodaytheresult of divergent or convergent evolution, and (2) did the multidomain-muWunctional protein genes arise by duplications of a primordial gene or by fusion of unrelated ancestral genes? Evidently both kinds of events described in the second part of the question have taken place, and 1 found it useful to be presented with both in the span of the 350 or so pages of the book. However, 1 would have preferred a few

book reviews 7 more examples on the evolution of non- enzymatic proteins.

It is obvious that no clear answer can be given at present to the questions posed above, until more information is available about the function of those proteins whose structure and genomic organization has been elucidated. and more is known about the gene str&ture of the proteins for which the function is known: Fiiy. I enjoyed the editor’s last chapter, which 1 found succinct and stimulating - or was it because 1 had read all the other chapters 6rst?

DIMITRIS KIOUSSIS

GeneSbucfwreandExpres&n Croup, Nation- al Insh&uI? for Medical Research, The Ridgeway, Mill Hill. London NW7 IAA. UK.

Variations upon a theme by Paynini

A Genetic Switch: Gene Control and Phage b

by Mark Ptashne, Cell Press und Blackwell Scietztific Publications, 1986. 912.95(x + 128@ges) ISBNO86542315 6

In their blind quest to become true renaissance men, my colleagues demand the touchstone of bacteriophage A. The secrets of this ‘little organism’ are an essential part of the intellectual grail of the late 26th century. However, modem man has not the patience to dwell upon the learned journals - no kudos to be gained from this endeavour - his lectures are gleaned from ‘News and Views’. Those two pillars of wisdom Tke Bacteri@hzge Lmnbdtz (edited by A. D. Hershey, 1971) and Lumbda II (He&ix et ol., 1993) are too unpalatable for our man, even Herskowitz’s and Hagen’s review @nuu. Rev. Get&. 1980) taxes his poor pate.

The publication of any monograph devoted to h is therefore welcomed, but this one is a pleasure to read, written well with clarity and charm and illustrated with the boldness of Lichtenstein. It represents an important contibution to _ the scientific literature, aiming at the enthusiastic but non-expert reader and succeeding. The enthusiasm of the author for his subject is all too evident in the text, but unlike in most scientillc texts, where enthusiasm clouds the general story, Ptashue bas not tripped over the minutiae of experimental detail - calmly distancing the reader from these facts: they should remain in the ‘learned journals’ where they belong. A com- parison might be made with the recent successful multi-authored text Molecular Biology of tb Cell (Alberts et al. 1983), which has been surprisingly so popular, but whilst Ptashne works out at 11.67~ per page and Alberts at 1.74~ per page

there is no contesz Ptashne wins. The book is organized into four

chapters of text with three appendices that draw together the experimental data into a unifying hypothesis. An introduc- tion gives the non-specialist a general resumk of the terminology of molecular biology and the speci6c language of bacteriophage A The reader must be prepared to have some of these defini- tions changed by the end of the book, for example DNA starts as a rigid rod and ends up bending. The centml theme of the book is the strategy employed by bacteriophage h in regulating the decision between lytic and lysogenic growth. The key molecules are the repressor protein and the cro protein and it is the interaction of these with their respective DNA binding sites that constitute the switch. The repressor and cro proteins share many features and an understand- ing of these two DNA biding proteins has given us a foundation for studies of the more subtle interactions that may control development and gene expres- sion in higher organisms. Certainly an effort is made to justify the behaviour of these two proteins, together with RNA

polymerase molecules, as the new paradigm for gene expression. Justitica- tion is made by reference to some clever experiments in Saccharomyces cerevisitze. In my youth the paradigm was the lactose operon, whichledMonod topostulate that what was true ofE. coliwould also be true of elephants. Now it appears that what is true of 1 is also true of yeast. However, the pretension that tbe repressor gene is analogous to a homeotic gene finds little sympathy with certain Europeans who work with Drosophila.

What about the other genes of 1 and even those of the host that are important in the lysis-lysogeny decision? The s&en&&ion- factors N and Q are brieflv introduced. as is ~11. but here the desciption is too sketchy. And ~11’s little minder. cl& is almost ignored. Similarly the role of the host and the SOS system is only briefly summarized. These are really only grumblings of a pedant, as I know that the punters thoroughly enjoyed this book. It was am’ is the recommended text for my second year Lambda course.

PHILIP OLIVER

Department of Genetics, llniversily of Cam- an&?, Cambt@e CB2 3EH. UK.

Coming soon, in Trends in Genetics

Glycosylation mutantsand the functions of mammalian carbohydrates

by Pamela Stanley

Glycosylation mutants of mammalian cells synthesize novel carbo- hydrate sfructures that are expressed on cellular glycoconjugates. Such mutants provide many avenues for investigating the func- tions of carbohydrates, both in their association with individual glycoconjugates (endogenous or introduced into the cell) and as an array of structures expressed at the surface of the cell.