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Targeted σ factor turnover inserts negative control into a positive feedback loop
Author(s) -
Donohue Timothy J.
Publication year - 2009
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2009.06823.x
Subject(s) - sigma factor , regulon , biology , sigma , streptomyces coelicolor , operon , gene , genetics , cytoplasm , microbiology and biotechnology , protease , proteolysis , gene expression , enzyme , biochemistry , promoter , mutant , physics , quantum mechanics
Summary Since their classification as members of the σ 70 superfamily, Group IV alternative σ factors have been found to control gene expression in response to diverse environmental or stress signals. Activity of the Streptomyces coelicolor Group IV family member, σ R (SigR), is increased by changes in the oxidation‐reduction state of cytoplasmic disulphide bonds. Once released by its cognate anti‐σ factor RsrA, σ R activates expression of gene products that help cells reduce cytoplasmic disulphide bonds. In this issue of Molecular Microbiology , Kim and co‐workers provide new insights into positive and negative control of σ R activity. The authors show that a transcript derived from the inducible σ R ‐dependent sigRrsrA p2 promoter operon encodes a σ R protein of a higher molecular weight (termed σ R′ ) than is found in uninduced cells. One major difference between σ R′ and the smaller σ R protein found in uninduced cells is the rapid proteolysis of σ R′ by the ClpP1/P2 protease system. The genes for the ClpP1/ClpP2 protease subunits are themselves members of the σ R regulon. The newly identified positive (σ R′ synthesis) and negative control (selective σ R′ turnover) aspects of this circuit are either found or predicted to exist in other related Group IV σ factor family members.