Mycobacterium smegmatis PafBC is involved in regulation of DNA damage response. Issue 1 (December 2017) - Fudrini Olivencia, Begonia
Abstract Two genes, pafB andpafC, are organized in an operon with the Pup-ligase genepafA, which is part of the Pup-proteasome system (PPS) present in mycobacteria and other actinobacteria. The PPS is crucial forMycobacterium tuberculosis resistance towards reactive nitrogen intermediates (RNI). However, pafB andpafC apparently play only a minor role in RNI resistance. To characterize their function, we generated apafBC deletion inMycobacterium smegmatis (Msm) . Proteome analysis of the mutant strain revealed decreased cellular levels of various proteins involved in DNA damage repair, including recombinase A (RecA). In agreement with this finding, Msm ΔpafBC displayed increased sensitivity to DNA damaging agents. In mycobacteria two pathways regulate DNA repair genes: the LexA/RecA-dependent SOS response and a predominant pathway that controls gene expression via a LexA/RecA-independent promoter, termed P1. PafB and PafC feature winged helix-turn-helix DNA binding motifs and we demonstrate that together they form a stable heterodimerin vitro, implying a function as a heterodimeric transcriptional regulator. Indeed, P1-driven transcription ofrecA was decreased inMsm ΔpafBC under standard conditions and induction ofrecA expression upon DNA damage was strongly impaired. Taken together, our data indicate an important regulatory function of PafBC in the mycobacterial DNA damage response.