Transcriptional and post-transcriptional regulation of whiB6 by a response regulator PhoP and a small noncoding RNA MTS1338 in Mycobacterium tuberculosis.

WhiB6 in pathogenic mycobacteria is highly upregulated during NO stress, hypoxia, and macrophage infection. Its expression primarily results from transcriptional control by a two-component response regulator PhoP in response to the various stresses exerted on mycobacterial cells inside phagosomes. Herein, we investigated the transcriptional and posttranscriptional regulatory mechanism of whiB6 expression. We found that PhoP binds to the PhoP-signature sequences located upstream to the core promoter region of whiB6 gene and controls its expression at the transcriptional level. Phosphorylation of PhoP is obligatory for binding to whiB6 promoter. A dormancy regulatory factor DosR, although doesn't bind to whiB6 gene, can bind to the PhoP-bound whiB6 gene implicating its potential role in whiB6 expression. A virulence-associated sRNA MTS1338 directly binds to the coding region of whiB6 gene presumably protecting it from cellular ribonucleases. Induction of MTS1338 in response to low pH and oxidative stress increases whiB6 accumulation likely through the stabilization of whiB6 transcript at the posttranscriptional level. This study substantially increases our knowledge of the regulation of whiB6 expression in M. tuberculosis.