Figure 1. Scheme showing redox homeostasis loop for the RsrA–σ^R complex.

The figure highlights the zinc coordination residues in reduced RsrA (RsrA^red.Zn²⁺) from Streptomyces coelicolor. Disulfide stress results in the loss of zinc and formation of a degenerate trigger disulfide bond in RsrA^ox, formed by the same zinc-binding residues. The transcribed regulon of σ^R includes anti-oxidant genes that re-establish redox homeostasis and the genes for sigR and rsrA (not shown), which amplify the response. Not shown is an additional layer of regulation involving a form of σ^R with an N-terminal extension that also binds RsrA, but is rapidly degraded by proteolysis⁶⁵. Shaded panels denote NMR structures of RsrA reported in the present work.