The Rip1 Protease of Mycobacterium tuberculosis Controls the SigD Regulon

<jats:title>ABSTRACT</jats:title> <jats:p> Regulated intramembrane proteolysis of membrane-embedded substrates by site-2 proteases (S2Ps) is a widespread mechanism of transmembrane signal transduction in bacteria and bacterial pathogens. We previously demonstrated that the <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Mycobacterium tuberculosis</jats:named-content> S2P Rip1 is required for full virulence in the mouse model of infection. Rip1 controls transcription in part through proteolysis of three transmembrane anti-sigma factors, anti-SigK, -L, and -M, but there are also Rip1-dependent, SigKLM-independent pathways. To determine the contribution of the sigma factors K, L, and M to the Δ <jats:italic>rip1</jats:italic> attenuation phenotype, we constructed an <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">M. tuberculosis</jats:named-content> Δ <jats:italic>sigK</jats:italic> Δ <jats:italic>sigL</jats:italic> Δ <jats:italic>sigM</jats:italic> mutant and found that this strain fails to recapitulate the marked attenuation of Δ <jats:italic>rip1</jats:italic> in mice. In a search for additional pathways controlled by Rip1, we demonstrated that the SigD regulon is positively regulated by the Rip1 pathway. Rip1 cleavage of transmembrane anti-SigD is required for expression of SigD target genes. In the absence of Rip1, proteolytic maturation of RsdA is impaired. These findings identify RsdA/SigD as a fourth arm of the branched pathway controlled by Rip1 in <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">M. tuberculosis</jats:named-content> . </jats:p>