Peering into the Natural Genetic Engineering Toolbox

Peering into the Natural Genetic ligate themselves to DNA also mediate the relatively new Engineering Toolbox phenomenon of rolling-circle transposition, as illustrated by the bacterial IS91 element (M Pilar Garcillá n-Barcia et al.). Rolling circle transposition also occurs in Mobile DNA II eukaryotes and is significant because it generates the The amazing and rapidly growing family of rearrangements mediated via diverse nucleophilic attacks The draft human genome tells us that our hereditary by 3Ј hydroxyl groups in strictly DNA mobility are de-material contains over 43% transposable and retro-tailed for prokaryotes and eukaryotes. Like the study of transposable elements. Our evolutionary history has catalytic RNA, advances in our understanding of DNA thus encompassed literally hundreds of thousands of rearrangements alter our thinking about the functional transposition events and other DNA rearrangements. roles of proteins and nucleic acids. DNA is clearly an Clearly, if we are to understand how we (and all other active participant in its own restructuring, and transpos-living organisms) evolved, we must come to terms with ases often function as chaperones to hold nucleic acid the importance of genetic mobility. In this sense, the chains in position to carry out phosphodiester bond publication of Mobile DNA II by the ASM Press earlier reshuffling. This is especially clear in the chapter on this year is very timely indeed. Tn5, where we have the most detailed structural knowl-This most recent collection of papers comes at a criti-edge of the transposition process (W. Reznikoff). cal transition point in our understanding of mobile ge-The RNA-based elements expand our mechanistic ho-netic elements (MGEs) and other aspects of natural ge-rizons further, beyond what was envisioned when re-netic engineering. The first volume on this subject (DNA verse transcription was first discovered. At the start of Insertion Elements, Plasmids and Episomes, Bukhari et the reverse transcription cycle, it is intriguing that LTR-al., CSH Press, 1976) appeared when transposition and containing retrotransposons have evolved at least two site-specific exchanges were still widely thought of as different methods for priming synthesis of the first cDNA " illegitimate recombination " —arcane marginal phenom-strand from LTR sequences: binding a tRNA or other ena largely confined to prokaryotes. Subsequent books small RNA primer, as in retroviruses, and self-priming 1989) marked a general recognition that DNA mobility direct relationship to mobile DNA elements because is ubiquitous throughout the kingdoms of life, albeit still their integrases use the same mechanism as transpos-within the conceptual …