Response Sigma Factor Research Articles

PG1659 functions as anti-sigma factor to extracytoplasmic function sigma factor RpoE in Porphyromonas gingivalis W83.

Anti-sigma factors play a critical role in regulating the expression of sigma factors in response to environmental stress signals. PG1659 is cotranscribed with an upstream gene PG1660 (rpoE), which encodes for a sigma factor that plays an important role in oxidative stress resistance and the virulence regulatory network of P. gingivalis. PG1659, which is annotated as a hypothetical gene, is evaluated in this study. PG1659, composed of 130 amino acids, is predicted to be transmembrane protein with a single calcium (Ca2+ ) binding site. In P. gingivalis FLL358 (ΔPG1659::ermF), the rpoE gene was highly upregulated compared to the wild-type W83 strain. RpoE-induced genes were also upregulated in the PG1659-defective isogenic mutant. Both protein-protein pull-down and bacterial two-hybrid assays revealed that the PG1659 protein could interact with/bind RpoE. The N-terminal domain of PG1659, representing the cytoplasmic fragment of the protein, is critical for interaction with RpoE. In the presence of PG1659, the initiation of transcription by the RpoE sigma factor was inhibited. Taken together, our data suggest that PG1659 is an anti-sigma factor which plays an important regulatory role in the modulation of the sigma factor RpoE in P. gingivalis.

Integrated activities of two alternative sigma factors coordinate iron acquisition and uptake by Pseudomonas aeruginosa.

Alternative sigma (σ) factors govern expression of bacterial genes in response to diverse environmental signals. In Pseudomonas aeruginosa σPvdS directs expression of genes for production of a siderophore, pyoverdine, as well as a toxin and a protease. σFpvI directs expression of a receptor for ferripyoverdine import. Expression of the genes encoding σPvdS and σFpvI is iron-regulated and an antisigma protein, FpvR20 , post-translationally controls the activities of the sigma factors in response to the amount of ferripyoverdine present. Here we show that iron represses synthesis of σPvdS to a far greater extent than σFpvI . In contrast ferripyoverdine exerts similar effects on the activities of both sigma factors. Using a combination of in vivo and in vitro assays we show that σFpvI and σPvdS have comparable affinities for, and are equally inhibited by, FpvR20 . Importantly, in the absence of ferripyoverdine the amount of FpvR20 per cell is lower than the amount of σFpvI and σPvdS , allowing basal expression of target genes that is required to activate the signalling pathway when ferripyoverdine is present. This complex interplay of transcriptional and post-translational regulation enables a co-ordinated response to ferripyoverdine but distinct responses to iron.

The sigma factors of Mycobacterium tuberculosis: regulation of the regulators

One of the important determinants of virulence of Mycobacterium tuberculosis is adaptation to adverse conditions encountered in the host cells. The ability of Mycobacterium to successfully adapt to stress conditions is brought about by the expression of specific regulons effected by a repertoire of sigma factors. The induction and availability of sigma factors in response to specific stimuli is governed by a complex regulatory network comprising a number of proteins, including sigma factors themselves. A serine-threonine protein kinase-mediated signaling pathway adds another dimension to the mycobacterial sigma factor regulatory network. This review highlights the recent advances in understanding mycobacterial sigma factors, their regulation and contribution to bacterial pathogenesis.

Assignment of the Zinc Ligands in RsrA, a Redox-Sensing ZAS Protein from Streptomyces coelicolor

ZAS proteins are widespread bacterial zinc-containing anti-sigma factors that regulate the activity of sigma factors in response to diverse cues. One of the best characterized ZAS proteins is RsrA from Streptomyces coelicolor, which responds to disulfide stress. Zn-RsrA binds and represses the transcriptional activity of sigmaR in the reducing environment of the cytoplasm but undergoes reversible, intramolecular disulfide bond formation during oxidative stress. This expels the single metal ion and causes dramatic structural changes in RsrA that result in its dissociation from sigmaR, leaving the sigma factor free to activate the transcription of antioxidant genes. We showed recently that Zn2+ serves a critical role in modulating the redox activity of RsrA thiols but uncertainty remains as to how the metal ion is coordinated in RsrA and related ZAS proteins. Using a combination of random and site-specific mutagenesis with zinc K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, we have assigned unambiguously the metal ligands in RsrA, thereby distinguishing between the different ligation models that have been proposed. The data show that the zinc site in RsrA is comprised of Cys11, His37, Cys41, and Cys44. Three of these residues are part of a conserved ZAS-specific sequence motif (H37xxxC41xxC44), with the fourth ligand, Cys11, found in a subset of ZAS proteins. Cys11 and Cys44 form the trigger disulfide in RsrA, explaining why the metal ion is expelled during oxidation. We discuss these data in the context of redox sensing by RsrA and the sensory mechanisms of other ZAS proteins.

Interactions of anti-sigma factor antagonists of Mycobacterium tuberculosis in the yeast two-hybrid system

Anti-sigma factor antagonists (anti-anti-sigma factors) play critical roles in regulating the expression of alternative sigma factors in response to specific stress signals. The Clusters of Orthologous Groups (COG) database has identified the existence of six genes, Rv0516c, Rv1364c, Rv1365c, Rv1904, Rv2638 and Rv3687c (grouped under the cluster COG1366), encoding potential anti-sigma factor antagonists in Mycobacterium tuberculosis. These molecules are speculated to regulate the expression of sigma factor SigF of M. tuberculosis in response to stress signals. Since signaling occurs via physical interactions of proteins (protein-protein interaction), we investigated whether the anti-sigma factor antagonists of M. tuberculosis interact with anti-sigma factor RsbW (Rv3287c) or the sigma factor SigF (Rv3286c) in the yeast two-hybrid system. The results revealed that most of the anti-sigma factor antagonists interact with either RsbW or SigF or both. In addition, some anti-sigma factor antagonists also displayed limited interactions between themselves. These interactions suggest that they possibly transduce some signals to SigF and between themselves.