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Expanding the Horizon of Recombination Repair in Mycobacteria: Identification and Characterization of Novel Proteins

In prokaryotes, repair by homologous recombination provides a major means to reinstate the genetic information lost in DNA damage. Recent research on recombination repair in mycobacteria has led to significant revision of the understanding of this system. A comparative analysis of the system, carried out in 43 mycobacterial genomes, lead to identification of novel proteins. To substantiate the predictions, biochemical and structural investigations on probable roles of two proteins, namely, SSBb and RecGwed, were carried out. The structure of M. smegmatis SSBb (MsSSBb), was determined at 2.5 □ resolution. Solution studies indicate that the canonical SSB (MsSSBa) is more stable towards thermal and chemical denaturation than MsSSBb. Also, MsSSBa has a two‐fold higher DNA binding affinity than MsSSBb. A direct physical interaction between MsSSBb and MsRecA was established, suggesting a role during recombination. The expression levels of ssbB gene increased by approximately two‐ and sevenfold in UV and hypoxic stress, respectively, while concurrently the levels of ssbA expression declined. These results indicate a role of MsSSBb in recombination repair during stress. MsRecGwed binds a variety of branched DNA structures in vitro, while it does not bind ss‐ or dsDNA. The up‐regulation of recGwed during UV damage, and down‐regulation during H2O2/MMS stress, in M. smegmatis indicated a possible role in post‐replicative recombination events that proceed though branched DNA intermediates. Taken together, this work augments the understanding of the repertoire of proteins known to be involved in DNA repair pathways in mycobacteria.