Characterisation of the Mycobacterium tuberculosis alternative sigma factor SigG: Its operon and regulon

A major step in the pathogenesis of Mycobacterium tuberculosis is the ability to survive inside macrophages, where it is exposed to a number of DNA damaging agents. The alternative sigma factor SigG has been shown to be upregulated by DNA damaging agents and by macrophage infection, but not to regulate genes of the DNA repair pathway. Here we show that SigG is expressed from at least two promoters, the most dominant of these being the DNA damage inducible RecA_Ndp promoter. This promoter is located within the annotated coding region of SigG and so the correct translational start site was determined experimentally and found to be 114 bp downstream of the annotated start site. Examining the gene expression profile of a SigG over-expression strain found a small number of genes to up-regulated, two of these encoded proteins containing glyoxylase-like domains.