The low incidence of diversity-generating retroelements in sequenced genomes.

The insertion of a retrotransposable element is usually associated with adverse or, at best, neutral effects on the host. Diversity-generating retroelements (DGRs) are the first elements that seem to offer a direct selective advantage to their phage or prokaryote host by exact replacement of a short, defined region of a host gene with a hypermutated variant. In a previous study, we presented the software DiGReF for identification of DGRs in genome sequences, and compiled the first comprehensive set of diversity-generating retroelements in public databases. We identified 155 elements in more than 6000 prokaryotic and phage genomes, which was a surprisingly low number. In this commentary, we will discuss the low incidence of these elements and speculate about the biological role of bacterial DGRs.