SigRdependent

SigRdependent refers to genes and transcriptional programs controlled by the sigma factor SigR, an extracytoplasmic function (ECF) sigma factor found in actinobacteria such as Streptomyces and related genera. SigR directs RNA polymerase to promoters of a redox- and thiol-disulfide stress regulon, enabling rapid

transcriptional responses to oxidative challenge and thiol-oxidative stress.

The activity of SigR is tightly regulated by an anti-sigma factor, commonly RsrA. Under non-stress conditions, RsrA binds SigR and prevents transcription of SigR-dependent genes. Upon oxidative stress or thiol-disulfide imbalance, RsrA undergoes conformational changes or oxidation, releasing SigR. Free SigR can then associate with RNA polymerase and activate transcription of target genes. Once the stress subsides, RsrA is reduced and rebinds SigR, returning the system to the off state.

The SigR regulon typically includes genes involved in maintaining redox balance and protein homeostasis, such as thioredoxin and disulfide-reducing systems, redox chaperones, and proteases. In some species, SigR-dependent promoters have characteristic recognition sequences that confer specific promoter binding, though exact motifs can vary between organisms.

Functional significance of SigRdependent transcription lies in its ability to mount a rapid, coordinated response to oxidative and thiol-oxidative stress, preserving protein folding, preventing aggregation, and supporting survival in challenging environments. The term is often used to denote genes whose expression is directly regulated by SigR as part of its regulon, and to distinguish them from genes governed by other sigma factors.