FIG. 3.

Redox regulation of the Zn-binding antisigma factor RsrA of Streptomyces coelicolor. RsrA is a zinc-binding, redox-sensitive anti-σ factor that sequesters σ^R under reducing conditions. Diamide treatment causes intramolecular disulfide-bond formation in RsrA, resulting in the release of Zn(II) and active σ^R. Free σ^R activates transcription of σ^R regulon genes, including trxBA and trxC (thioredoxin and thioredoxin reductase), mshA (a glycosyltransferase catalyzing the first step in MSH synthesis), and mca (mycothiol-S-conjugate amidase). Collectively, these thiol-reducing systems function in reduction of oxidized RsrA and restore the thiol redox balance. σ^R and the unstable σ^R′protein (with a destabilizing N-terminal extension) are positively autoregulated (see text).