Sigma factor-anti-sigma factor interaction in alginate synthesis: inhibition of AlgT by MucA

Abstract

Conversion from the nonmucoid to the mucoid phenotype is a typical feature of Pseudomonas aeruginosa strains causing chronic pulmonary infections in cystic fibrosis patients. One of the key genetic controls in this conversion to mucoidy is from the algT(U)-mucA-mucB(algN) locus, located at 67.5 min on the standard P. aeruginosa chromosomal map. The algT gene promotes conversion to mucoidy and encodes an alternative sigma factor ( E ) which belongs to the ECF (for extracytoplasmic function) family. On the other hand, the mucA and mucB (algN) genes suppress conversion to mucoidy. Loss-of-function mutations in mucA have been postulated to be the cause of mucoidy in some P. aeruginosa strains isolated from cystic fibrosis patients. We expressed and purified the protein products from the mucA and mucB open reading frames. The purified MucA protein abolishes the in vitro transcription specified by AlgT and the ability of AlgT to compete with an Escherichia coli sigma factor, FliA, suggesting that inhibiting AlgT-dependent transcription could be the mechanism by which mucA suppresses mucoidy in vivo. Enzyme-linked immunosorbent assay and glycerol density gradient sedimentation experiments suggest that MucA physically interacts with AlgT.

Microbial pathogenesis in cystic fibrosis: co‐ordinate regulation of heat‐shock response and conversion to mucoidy in Pseudomonas aeruginosa

“…MucA has been demonstrated to negatively regulate AlgU (Fig. 6A) and recent findings support the hypothesis that it does so by binding to AlgU (Martin et al, 1993c;Schurr et al, 1994;Xie et al, 1996). Since MucA, as shown here, also controls expression of rpoH it will be of interest to examine, in future studies, the extent of the effects of mucA mutations on the expression of rpoH-dependent genes.…”

“…AlgU activity is controlled at a post-translational level by the products of the downstream genes (mucABCD ) that encode its negative regulators. Recently, it has been demonstrated that MucA probably functions as an anti-sigma factor Xie et al, 1996). Mutations in mucA and other muc genes located in the 67.5 min region are responsible for the conversion to mucoidy in CF isolates and laboratory strains (Martin et al, 1993c).…”

The nucleoside diphosphate kinase of Mycobacterium smegmatis: identification of proteins that modulate specificity of nucleoside triphosphate synthesis by the enzyme

“…A. Glycerol-gradient analysis of the complex formation between proteins P 70 , P 65 , P 60 and P 50 and the mycobacterial NdK. The glycerol gradient was prepared as described previously (Sundin et al, 1996a;Xie et al, 1996) and briefly in the Experimental procedures. Lanes have been marked according to the samples they represent; anti-Ndk antibodies were used at a dilution of 1:500 in the dot blot Western analysis.…”

“…ᮊ 1997 Blackwell Science Ltd, Molecular Microbiology, 24, [477][478][479][480][481][482][483][484][485][486][487] Complex-formation analysis with glycerol-gradient centrifugation Glycerol-gradient centrifugation was carried out by a modification of the method developed by Bowman et al (1981) as described previously (Sundin et al, 1996a;Xie et al, 1996). A batch gradient of glycerol was prepared by successive layering of 60%, 50%, 40%, 30%, 20%, 10% and 5% solutions of glycerol in volumes of 1 ml in Beckman 10 ml ultracentrifuge tubes.…”

The HtrA family of serine proteases

“…RseC, another inner membrane protein, can also modulate RpoS activity, again via an unknown mechanism (Missiakas and Raina, 1997a). There is experimental evidence for a system similar to the RseABC/RpoE network in Pseudomonas aeruginosa, and homologues exist in several other Gram-negative bacterial species, suggesting that similar regulatory mechanisms are relatively conserved in evolutionary terms Schurr et al, 1996;Xie et al, 1996).…”