The Mycoplasma genitalium MG352-encoded protein is a Holliday junction resolvase that has a non-functional orthologue in Mycoplasma pneumoniae

Recombination between repeated DNA elements in the genomes of Mycoplasma species appears to lie at the basis of antigenic variation of several essential surface proteins. It is therefore imperative that the DNA recombinatorial pathways in mycoplasmas be unravelled. Here, we describe the proteins encoded by the Mycoplasma genitalium MG352 and Mycoplasma pneumoniae MPN528a genes (RecU Mge and RecU Mpn respectively), which share sequence similarity with RecU Holliday junction (HJ) resolvases. RecU Mge was found to: (i) bind HJ substrates and large double-stranded DNA molecules and (ii) cleave HJ substrates at the sequence 5'- G / T C↓ C / T T A / G G-3' in the presence of Mn 2+ . Interestingly, RecU Mpn (from M. pneumoniae subtype 2 strains) did not possess obvious DNA binding or cleavage activities, which was found to be caused by the presence of a glutamic acid residue at position 67 of the protein, which is not conserved in ReCU Mge . Additionally, RecU Mpn appears not to be expressed by subtype 1 M. pneumoniae strains, as these possess a TAA translation termination codon at position 181-183 of MPN528a. We conclude that RecU Mge is a HJ resolvase that may play a central role in recombination in M. genitalium.