20 Reverse Transcription and Evolution

Abstract

Originally discovered as part of the retrovirus life cycle, reverse transcription is now known to play a number of roles in biology: in the replication of several groups of viruses, in the mobilization of retrovirus-like and other transposable elements, in the generation of chromosomal ends, and in other contexts yet to be understood. The previous chapters described the specific biological and biochemical systems within which reverse transcriptase is found and the possible relationships among these systems and their origins. Here, I focus on the role of reverse transcription in the evolution of the elements that rely on it for replication as well as the role of these elements in the evolution of their hosts.

Like much of evolutionary biology, this discussion will include speculation and reliance on untested assumptions. In at least one respect, we are fortunate. The high error rates of retroviral reverse transcriptases, combined with the relatively short generation times of the genomes they replicate, provide observable evolutionary changes in experimentally tractable time frames. Lessons learned from this sort of change can illuminate the larger evolutionary picture. Thus, in experimental time, we can observe the acquisition and loss of viral genes, the evolution of populations by accumulation of mutation and recombination events, and the effects on the host cell and organism of the insertion of reverse transcripts into the genome. For these reasons, this discussion concentrates on retroviruses, with reference to some less easily studied systems — LINEs and pseudogenes —which are products of reverse transcription and constitute a...