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apparently take only a single base mutation at the 3' splice site to convert some of them into nuclear- type introns, with signals appropri- ate for splicing by snRNPs. So, while several authors in this volume suggest that the nuclear splicing machine D - evolved from something resembling group II introns, it is also quite possible that many or all of the individual nuclear introns evolved from self- inserted group II introns.

What, then, were the original units of protein structure? Apart from the 'RNA world', this volume is also a valuable compendium of information relevant to the early 'protein world' - on the simplest and most widespread types of domain in proteins. Here are zinc fingers, for binding nucleic acids (Klug and Rhodes; Berg); EF hands, for binding calcium (Kretsinger); anion holes, for binding triphos- phates (Schulz); as well as larger but no less widespread domains such as serine proteases, several families of protease inhibitors, and globins. All these domain types are reviewed, in most cases with usefffl up-to-date compilations or consen- suses of sequences, and with information on the three- dimensional structures that they adopt.

Various other topics in the origin of cells are also covered, from both before and after the origin of ribozymes and proteins. The origin of RNA itself in a primordial soup is still a problem, and perhaps an insoluble one (Miller; Orgel); it seems easier to make glycero-nucleic acids (with glycerol instead of ribose) and evolve RNA from them. Weiner comments: 'We simply cannot skip the soup and start with the main course'. The origin of cell mem- branes is considered only by Cavalier-Smith, as part of a com- prehensive scenario for the entire evolution of life: he makes the attractive suggestion that the major components of life as we know it (including RNA, DNA, proteins, and proton pumping) developed on the outside of lipid vesicles or 'obcells', which only latterly became enclosed. (Surprisingly, given the title, this volume has no other contributions concerning the origins of bioenergetics.) At later

epochs, the divergence of the major extant forms of life should be accessible to study by rRNA sequence phylogeny, and both Olson and Lake give valuably clear reviews of the analytic methods and their pitfalls, but reach opposite conclusions about the validity of the 'archaebacteria'.

As for catalysis: it will be an ironic reversal of a 3-billion-year

The Heritage of Experimental Embryology: Hans Spemann

and the Organiser by Viktor Hamburger. Oxford Lnivers W Press,

1988. £22.50 (xii + 196 pages) ISBN 0 19 505110 6

Viktor Hamburger has set out, in what seems to me an admirable blend of scientific and biographical (including autobiographical) discourse, to chart the key experi- ments in the careers of Hans Spemann and his students, and the interpretation made of them. The story spreads from the Germany of the inter-war years to the North America and, to a lesser extent, the Europe and Japan of the following two decades.

It is an invaluable book for scholarly minded students of ani- mal development. Hamburger's avuncular tone makes for gentle and easy reading; his German culture shows, to advantage, in his unseasonable devotion to abstract ideas about the forms of things (fields, potencies and the like). But he has lost, if he ever had it, the high-German style of writing.

This is unsurprising; he has after all had a long and rather suc- cessful career making himself plain to US developmental neurobiol- ogists, having arrived there in 1932 after leaving the milieu he recol- lects in his book. Those undemo- cratic-spirited enough to recognize that 'progress' has not been accom- panied by actual advance in avail- able physical and cultural quality of

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old evolutionary decision if ribozymes, redesigned as Uhlenbeck's group show to be possible (Sampson et al.), become the tool of choice for experimental manipulation of genes.

JOHN ROGERS

Department of PbrsioloRy, l'nh:ersi(y o/ Cambridge. Cambn'dge CB2 .$E(;, g X.

life, even for the privileged, will be engaged by the description of the student and laboratory life that attended the scientific sto U. This is an apposite part of the book's mes- sage, The raw power of the techni- cal tools for understanding that is now available to biologists is inde- scribably greater than was available to its drarna t i sper sonae but only now, essentially a half-centu W later, is our understanding of the 'organ- izer' phenomenon perhaps about to be pushed significantly beyond what was then arrived at.

Various extraordina W facts emerge, not widely known among non-German-reading contemporary embryologists, which emphasize the heroic texture of the research. Before the discovery of simple saline media that would support the physiology of amphibian embryo cells once their surface layer was breached, filtered tap water was the inevitable medium for the grafting operations (appar- ently Wurtzburg water was - is? - especially favourable!). In conse- quence, an able student can now successfully perform - whatever the morphological results - more Spemann-type operations in one day than were ever reared tar enough by the master and his disciples to be analysed, an analysis that. years later, led to core developmental biology's one Nobel Prize.

Added to this was another feature somehow suited to, but also perhaps contributing to, the singu- lar character of the work and of the pantheon of individualists who pursued it: the seasonal nature of the raw material. Imagine a biology laboratory where essentially all the data accrued during a few weeks of intensive activity, which included collecting eggs, sorting, operating,

f ~ ' ] O O K [ ~ E V I E W S

attempting to rear, and sectioning survivors. In many seasons, even less information than had been planned on was successfully gar- nered, yet 'lab life' for the remain- der of the year appears to have been essentially the social process of wondering what the information meant and of pondering what, in view of that, to try and do next spring.

All this certainly fostered the making of much thought from a slender database, a trait that reached one of its highest expres- sions even among biologists in Spemann (even physicists don't do it now, while Darwin's oeuvre was after all data rich, and Freud is not currently a card-carrying natural scientist at High Table). But Spemann is no flanneler. Hamburger is meticulous in point- ing out the character of his thought, which was in a sense min- imalist in never pursuing an elabo- ration of results further than the observed phenomenon demanded. His immediate and later disciples have been better at building baroque edifices which may or may not turn our to correspond to actual mechanisms.

Another fascinating point brought out is how emerging knowledge is shaped, in that epoch more than now, by investigators' extra-scientific inclinations.

An aa.nce of ai h'sls

Genetic Recombination

edited by Raju Kucherlapati and Gerald R. Smith, American Society, for Microbiology,

1988. $44.00 (ASM members), $65.00 (nonmembers) (xii + 731 pages)

ISBN 1 55581 004 7

As indicated in the brief preface to this book, it is convenient to classify recombination processes into three groups. First is the general type which forms the basis for all classical genetic analysis, in which homologous tracts of DNA must be present in the parental DNA in order that the initiation of

Spemann's predisposition for the whole embryo was so deep that he would not fundamentally depart from experimentation at this level even when the research would seem to have demanded it, where- as his student Holtfreter's lifetime inclination has been for the explant and the cell. Uniquely highly wrought experiments were thus generated.

In essence the book lays out what its title suggests; the heritage of concepts which - although we all might want to clarify them, and only insect development strangely has so far benefited - will be indis- pensable to understanding verte- brate development as opposed merely to cataloguing its molecular nuts and bolts. The key scientific findings and conclusions are better and more compactly laid out here than in any other adequate source. Textbooks now treat them perfunc- torily, and where they appear in specialist monographs, they tend to be interspersed with other not necessarily relevant 'stories'. The biographical bonus, even in its most implicitly personal sections, is a welcome one.

JONATHAN COOKE

National Institute for Medical Research. Mill Hill, London NW7 1AA, UK.

recombination can occur. Then there are site-specific systems that involve recognition between two short and not necessarily identical DNA sequences. Such mechanisms underlie the movement of trans- posons, the integration of viral genomes, and the excision and inversion of stretches of DNA within genomes. The third class is really a repository for what ge- nomic interactions are left, the so- called illegitimate events, in which novel DNA joints are produced in recombinant molecules. These usually occur at frequencies that are orders of magnitude less than in the general or site-specific categories, but can have important biological consequences, for example in producing the dupli- cation of genes that provides the potential for evolutionary change, and in the joining of double-

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stranded ends of DNA, which forms the basis for some kinds of repair and also for the integration of foreign DNA into eukaryote genomes.

Genetic Recombina t ion contains 24 articles covering different aspects of these three types of recombination. The first 12 deal with prokaryote examples, the latter 12 with eukaryote ones. All the articles are written by experts in the various fields, are lucid and up to date, and provide contem- porary assessments of their respective areas. Some topics are inevitably not represented, or mentioned only in passing. For example there is little about recom- bination among viruses, or about the role of recombination in the repair of genomic damage, or about in vitro studies on trans- position systems. Nonetheless the book contains a comprehensive collection of review articles coupled with extensive references. Undoubtedly it will be invaluable to geneticists of all persuasions as well as to teachers and students of advanced genetics courses.

However, although the book is a mine of information about genetic systems of present-day interest, it is rather short of insights into the biological function of recombination and the underlying relationships between the various specialized systems. Like nearly all the current multi-authored books it contains an abundance of analysis and a paucity of synthesis. There is still a crying need for some treat- ment of recombination which, among other topics, on the genetics side discusses its evol- utionary origins and implications, its various roles in viral and cell cycles, the association of meiosis with the division between prokary- otes and eukaryotes and the inter- play of the three types of recombi- nation in producing genetic diversity - and on the molecular side deals with topological prob- lems intrinsically related to recom- bination intermediates, and the types of enzymes that become implicated in their formation and resolution.

NEVILLE SYMONDS

School of Biological Sciences. University of Sussex, Brighton BN1 9QG UK.