The Anti-Anti-Sigma Factor BldG Is Involved in Activation of the Stress Response Sigma Factor σH in Streptomyces coelicolor A3(2) ▿

Abstract

The alternative stress response sigma factor σH has a role in regulation of the osmotic stress response and in morphological differentiation in Streptomyces coelicolor A3(2). Its gene, sigH, is located in an operon with the gene that encodes its anti-sigma factor UshX (PrsH). However, no gene with similarity to an anti-anti-sigma factor which may have a role in σH activation by a “partner-switching” mechanism is located in the operon. By using a combination of several approaches, including pull-down and bacterial two-hybrid assays and visualization of the complex by native polyacrylamide electrophoresis, we demonstrated a direct interaction between UshX and the pleiotropic sporulation-specific anti-anti-sigma factor BldG. Osmotic induction of transcription of the sigHp2 promoter that is specifically recognized by RNA polymerase containing σH was absent in an S. coelicolor bldG mutant, indicating a role of BldG in σH activation by a partner-switching-like mechanism