Expression of Mycobacterium tuberculosis pe_pgrs33 is repressed during stationary phase and stress conditions, and its transcription is mediated by sigma factor A

Although recent work shows that the expression of the PE/PE_PGRS protein family occur both in vitro and in vivo under stress conditions, very little is known about their promoter and how they are regulated. In this work, the promoter region of a member of PE_PGRS family, the PE_PGRS33 was identified and the promoter boxes were determined. To date, this is one of the few reports that describe a promoter region of a PE_PGRS member. In addition, the gene promoter functionality was assayed in Mycobacterium smegmatis with the green fluorescent protein reporter gene fused to different lengths of pe_pgrs33 promoter sequences. The GFP was down-regulated in the stationary phase, under nutrient starvation and oxygen depletion, suggesting that, in stress conditions, regulation of the gene could be under control of a repressor molecule. A 5′ rapid amplification of cDNA end assay of transcriptional fusions evaluated in M. smegmatis and in Mycobacterium tuberculosis mRNA revealed a transcription start point 75 nt upstream of the ATG codon and a −10 like-SigA box. Furthermore, a transcription run assay confirmed that SigA mediates in vitro transcription of pe_pgrs33. Interestingly, conserved −10 SigA boxes were found in the intergenic region of several PE_PGRS genes. These results suggest that expression of some PE_PGRS genes may be mediated by SigA, and the differences in expression observed in the gene family could be explained by the participation of additional regulatory genetic elements.