Integration and excision of the Mycobacterium tuberculosis prophage-like element, φRv1

Abstract

The genomes of Mycobacterium tuberculosis H37Rv and CDC1551 each contain two prophage-like elements, φRv1 and φRv2. The φRv1 element is not only absent from Mycobacterium bovis BCG but is in different locations within the two sequenced M. tuberculosis genomes; in both cases φRv1 is inserted into a REP13E12 repeated sequence, which presumably contains the bacterial attachment site, attB, for φRv1. Although φRv1 is probably too small to encode infectious phage particles, it may nevertheless have an active integration/excision system and be capable of moving from one chromosomal position to another. We show here that the M. tuberculosis H37Rv φRv1 element does indeed encode an active site-specific recombination system in which an integrase of the serine recombinase family (Rv1586c) catalyses integration and excision and a small, basic φRv1-encoded protein (Rv1584c) controls the directionality of recombination. Integration-proficient plasmid vectors derived from φRv1 efficiently transform BCG, can utilize four of the seven REP13E12 sites present in BCG as attachment sites, and can occupy more than one site simultaneously.