SIGMA-FACTOR ANTI-SIGMA FACTOR INTERACTION IN ALGINATE SYNTHESIS - INHIBITION OF ALGT BY MUCA

Conversion from the nonmucoid to the mucoid phenotype is a typical fea ture of Pseudomonas aeruginosa strains causing chronic pulmonary infec tions 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 s igma factor (sigma(E)) which belongs to the ECF (for extracytoplasmic function) family. On the other hand, the mucA and mucB (algN) genes su ppress conversion to mucoidy. Loss-of-function mutations in mucA have been postulated to be the cause of mucoidy in some P. aeruginosa strai ns isolated from cystic fibrosis patients. We expressed and purified t he protein products from the mucA and mucB open reading frames. The pu rified 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. Enzy me-linked immunosorbent assay and glycerol density gradient sedimentat ion experiments suggest that MucA physically interacts with AlgT.