| Structural highlights
Function
[SIGR_STRCO] Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. Extracytoplasmic function (ECF) sigma factors are held in an inactive form by an anti-sigma factor (RsrA) until released. Responds to thiol-oxidative stress, involved in regulation of about 30 genes and operons, including the thioredoxin system (trxB-trxA, trxC), ribosomal protein L31, RNA polymerase-binding protein RbpA and mycothiol (MSH) biosynthetic (mshA) and recycling genes (mca). In conjunction with its cognate anti-sigma factor RsrA may sense the intracellular level of reduced MSH.[1] [2] [3] [4]
Evolutionary Conservation
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Publication Abstract from PubMed
The extracytoplasmic function (ECF) sigma factor sigma(R) is a global regulator of redox homeostasis in the antibiotic-producing bacterium Streptomyces coelicolor, with a similar role in other actinomycetes such as Mycobacterium tuberculosis. Normally maintained in an inactive state by its bound anti-sigma factor RsrA, sigma(R) dissociates in response to intracellular disulphide-stress to direct core RNA polymerase to transcribe genes, such as trxBA and trxC that encode the enzymes of the thioredoxin disulphide reductase pathway, that re-establish redox homeostasis. Little is known about where RsrA binds on sigma(R) or how it suppresses sigma(R)-dependent transcriptional activity. Using a combination of proteolysis, surface-enhanced laser desorption ionisation mass spectrometry and pull-down assays we identify an N-terminal, approximately 10kDa domain (sigma(RN)) that encompasses region 2 of sigma(R) that represents the major RsrA binding site. We show that sigma(RN) inhibits transcription by an unrelated sigma factor and that this inhibition is relieved by RsrA binding, reaffirming that region 2 is involved in binding to core RNA polymerase but also demonstrating that the likely mechanism by which RsrA inhibits sigma(R) activity is by blocking this association. We also report the 2.4A resolution crystal structure of sigma(RN) that reveals extensive structural conservation with the equivalent region of sigma(70) from Escherichia coli as well as with the cyclin-box, a domain-fold found in the eukaryotic proteins TFIIB and cyclin A. sigma(RN) has a propensity to aggregate, due to steric complementarity of oppositely charged surfaces on the domain, but this is inhibited by RsrA, an observation that suggests a possible mode of action for RsrA which we compare to other well-studied sigma factor-anti-sigma factor systems.
Identification and structure of the anti-sigma factor-binding domain of the disulphide-stress regulated sigma factor sigma(R) from Streptomyces coelicolor.,Li W, Stevenson CE, Burton N, Jakimowicz P, Paget MS, Buttner MJ, Lawson DM, Kleanthous C J Mol Biol. 2002 Oct 18;323(2):225-36. PMID:12381317[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Kang JG, Paget MS, Seok YJ, Hahn MY, Bae JB, Hahn JS, Kleanthous C, Buttner MJ, Roe JH. RsrA, an anti-sigma factor regulated by redox change. EMBO J. 1999 Aug 2;18(15):4292-8. PMID:10428967 doi:http://dx.doi.org/10.1093/emboj/18.15.4292
- ↑ Paget MS, Molle V, Cohen G, Aharonowitz Y, Buttner MJ. Defining the disulphide stress response in Streptomyces coelicolor A3(2): identification of the sigmaR regulon. Mol Microbiol. 2001 Nov;42(4):1007-20. PMID:11737643
- ↑ Li W, Bottrill AR, Bibb MJ, Buttner MJ, Paget MS, Kleanthous C. The Role of zinc in the disulphide stress-regulated anti-sigma factor RsrA from Streptomyces coelicolor. J Mol Biol. 2003 Oct 17;333(2):461-72. PMID:14529630 doi:http://dx.doi.org/10.1016/S0022283603010763
- ↑ Paget MS, Kang JG, Roe JH, Buttner MJ. sigmaR, an RNA polymerase sigma factor that modulates expression of the thioredoxin system in response to oxidative stress in Streptomyces coelicolor A3(2). EMBO J. 1998 Oct 1;17(19):5776-82. PMID:9755177 doi:http://dx.doi.org/10.1093/emboj/17.19.5776
- ↑ Li W, Stevenson CE, Burton N, Jakimowicz P, Paget MS, Buttner MJ, Lawson DM, Kleanthous C. Identification and structure of the anti-sigma factor-binding domain of the disulphide-stress regulated sigma factor sigma(R) from Streptomyces coelicolor. J Mol Biol. 2002 Oct 18;323(2):225-36. PMID:12381317
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