Characterization of the operon encoding the Holliday junction helicase RuvAB from Mycoplasma genitalium and its role in mgpB and mgpC gene variation.

Mycoplasma genitalium is an emerging sexually transmitted pathogen associated with reproductive tract disease in men and women, and it can persist for months to years despite the development of a robust antibody response. Mechanisms that may contribute to persistence in vivo include phase and antigenic variation of the MgpB and MgpC adhesins. These processes occur by segmental recombination between discrete variable regions within mgpB and mgpC and multiple archived donor sequences termed MgPa repeats (MgPars). The molecular factors governing mgpB and mgpC variation are poorly understood and obscured by the paucity of recombination genes conserved in the M. genitalium genome. Recently, we demonstrated the requirement for RecA using a quantitative PCR (qPCR) assay developed to measure recombination between the mgpB and mgpC genes and MgPars. Here, we expand these studies by examining the roles of M. genitalium ruvA and ruvB homologs. Deletion of ruvA and ruvB impaired the ability to generate mgpB and mgpC phase and sequence variants, and these deficiencies could be complemented with wild-type copies, including the ruvA gene from Mycoplasma pneumoniae. In contrast, ruvA and ruvB deletions did not affect the sensitivity to UV irradiation, reinforcing our previous findings that the recombinational repair pathway plays a minor role in M. genitalium. Reverse transcription-PCR (RT-PCR) and primer extension analyses also revealed a complex transcriptional organization of the RuvAB system of M. genitalium, which is cotranscribed with two novel open reading frames (ORFs) (termed ORF1 and ORF2 herein) conserved only in M. pneumoniae. These findings suggest that these novel ORFs may play a role in recombination in these two closely related bacteria.