To be horizontally transferred or not

Abstract

Horizontal gene transfer is undoubtedly a major factor in prokaryotic genome evolution. However, not all genes are equally likely to be transferred: the probability of a gene being transferred is correlated with its function. Horizontal transfer has occurred frequently for operational (housekeeping) genes but rarely for informational genes involved in transcription, translation and related processes. Jain et al.1 Jain R. Rivera M.C. Lake J.A. Horizontal gene transfer among genomes: the complexity hypothesis. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 3801-3806 Crossref PubMed Scopus (879) Google Scholar investigated the temporal aspects of horizontal transfer using phylogenetic analysis of six complete prokaryotic genomes. They observed that operational genes have been horizontally transferred continuously since the divergence of the prokaryotes, rather than being exchanged in one, or a few, transfer events early in their evolution. In agreement with earlier studies, the differences in rates of evolution (measured by nucleotide substitution rates) between operational and informational genes are minimal, suggesting that factors other than the rate of evolution are responsible for the observed differences in horizontal transfer frequency. They propose that a major factor in the frequent horizontal transfer of operational genes is that, while informational genes are typically members of large, complex systems, operational genes are not; the horizontal transfer of informational genes is therefore less probable than that of operational genes.