A guide to the world of RNA: The RNA World: The Nature of Modern RNA Suggests a Prebiotic RNA (2nd Edn) edited by R.F. Gesteland, T.R. Cech and J.F. Atkins

Abstract

Cold Spring Harbor Laboratory Press, 1999. $129.00 (709 + xxv pages)ISBN 0 87969 561 7This is a new edition of a multi-author work whose first edition appeared in 1993. To quote from Crick’s foreword to the first edition (reprinted in this edition), ‘the “RNA World” originally referred to a hypothetical time in the evolution of earthly life when there was no elaborate mechanism of protein synthesis such as we have today’. Instead, it is envisaged that RNA molecules collectively had the capacity for self-replication as well as supplying other catalytic functions that were essential to evolving life. Evolution was rapid because RNA replication was not subject to proof-reading and error rates were inherently high.The idea that RNA, or something like it, was close to genesis seems almost inescapable from a rational perspective. However, we have no certain knowledge of that early era, only clues from the present-day world. There are differing views on the workings and metabolic sophistication of the RNA World, profound problems as to how it got started from prebiotic chemistry, and considerable difficulties in the progression to the world of genetically encoded, ribosomally synthesized proteins.This edition of The RNA World brings the reader abreast of current thinking on these great issues, with 24 chapters by leading workers of today’s ‘RNA World’ (including six Nobel Laureates, counting the writers of the foreword and prologue). Many chapters are updates from the earlier edition, but there are also some new chapters, and the text has been conveniently divided into three sections, namely: the origins of RNA and RNA at the origin; how to build a functional RNA; and transition to the RNP world.Very welcome among the new material is the opening chapter by Arrhenius and colleagues on the geophysical setting for early molecular evolution. Also new is chapter 9 by Gilbert and de Souza on introns in the RNA World; although this title may suggest a particular point of view, the chapter is a lucid exposition of much of the conceptual background to the RNA World, recommendable as an introductory read.A major avenue to increasing our knowledge of the catalytic potential of RNA comes from in vitro selection experiments. This approach may hold promise with regard to many biochemical processes that are handled in the modern world by proteins and cofactors, including redox and bioenergetic functions. Many years ago Fritz Lipmann wrote1xSee all References1, in the context of the origin of life, ‘the problem is to convert electron flux potential into phosphate bond potential…’. This prebiotic problem remains unsolved today, and it was tantalizing to see glimpses towards a solution, but only glimpses, in the chapter by Puglisi and Williams on RNA interaction with small ligands (including FAD and ATP) and in appendix 3 by Joyce, on reactions catalysed by RNA and DNA enzymes.These few comments leave much unsaid about this excellently compiled and informative volume. I write at the time of year when students are sitting examinations, and it occurs to me that a concise way in which to focus attention on some further points is to devise a few ‘essay’ or ‘short notes’ questions. (1) Does the cratering record of the moon set a limit to the age of life on earth? (see Ch. 1). (2) What do you understand by the term ‘Eigen error threshold’ in relation to genome size? (Ch. 2). (3) Were there always only four bases in the RNA World? (Ch. 6). (4) Give an evolutionary explanation for the fact that ribosomes from all sources consist of two subunits (Ch 8). (5) What do you understand by the term ‘intron’ in the RNA World before the advent of genetically encoded proteins? (Ch 9). (6) How versatile is RNA catalysis by present-day natural ribozymes? (Ch 13). (7) How might selenocysteine have become incorporated into the genetic code? (Ch 24). (8) Was the first eukaryote a ribo-organism? (May require further reading, e.g. 2xSogin, M. et al. : 167–184See all References, 3xPoole, A.M., Jeffares, D.C., and Penny, D. J. Mol. Evol. 1998; 46: 1–17Crossref | PubMed | Scopus (145)See all References). Please do not send your answers to me for marking!