Genome Biology and Evolution

Selfish genetic elements, suchas insertion sequences and transposons are found inmost genomes. Transposons are usually identifiable by their high copy number within genomes. In contrast, REP-associated tyrosine transposases (RAYTs), a recently described class of bacterial transposase, are typically present at just one copy per genome. This suggests that RAYTs no longer copy themselves and thus they no longer function as a typical transposase. Motivated by this possibility we interrogated thousands of fully sequenced bacterial genomes in order to determine patterns of RAYT diversity, their distribution across chromosomes and accessory elements, and rate of duplication.RAYTs encompass exceptionaldiversity andare divisible into at least five distinct groups. They possess featuresmore similar to housekeeping genes than insertion sequences, are predominantly vertically transmitted and have persisted through evolutionary timeto thepointwherethey arenowfoundin24%of all species forwhich at leastonefully sequencedgenomeis available.Overall, the genomic distributionof RAYTs suggests that they have been cooptedby host genomesto perform a function that benefits the host cell. © The Author 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution