Novel Mycobacterium tuberculosis anti-σ factor antagonists control σF activity by distinct mechanisms



The aetiological agent of tuberculosis, Mycobacterium tuberculosis, encodes 13 σ factors, as well as several putative anti-, and anti-anti- σ factors. Here we show that a σ factor that has been previously shown to be involved in virulence and persistence processes, σF, can be specifically inhibited by the anti-σ factor UsfX. Importantly, the inhibitory activity of UsfX, in turn, can be negatively regulated by two novel anti-anti-σ factors. The first anti-anti-σ factor seems to be regulated by redox potential, and the second may be regulated by phosphorylation as it is rendered non-functional by the introduction of a mutation that is believed to mimic phosphorylation of the anti-anti-σ factor. These results suggest that σF activity might be post-translationally modulated by at least two distinct pathways in response to different possible physiological cues, the outcome being consistent with the bacteria's ability to adapt to diverse host environments during disease progression, latency and reactivation.