SIGNAL TRANSDUCTION IN EXOPOLYSACCHARIDE ALGINATE SYNTHESIS - PHOSPHORYLATION OF THE RESPONSE REGULATOR ALGR1 IN PSEUDOMONAS-AERUGINOSA ANDESCHERICHIA-COLI

Synthesis of alginate by Pseudomonas aeruginosa correlates with its pa thogenicity in the lungs of patients suffering from cystic fibrosis (C F). Alginate synthesis-encoding genes (alg) in P. aeruginosa are norma lly silent, but are specifically triggered in the CF lung environment. The promoter for the algD gene, located at the upstream end of the al g cluster, is activated by environmental factors such as high osmolari ty, nutrient limitation and dehydration. Several regulatory proteins a re known to control transcription from the algD promoter. Among these proteins is AlgR1 which is homologous to the phosphorylation-dependent response regulators of the two-component signal transduction system. In this paper, we report that AlgR2, an 18-kDa protein which in cooper ation with AlgR1 regulates the algD promoter, undergoes phosphorylatio n in the presence of ATP. The phosphate group acquired by AlgR2 is the n transferred to AlgR1. In addition, we show that AlgR1 can be phospho rylated by an AlgR2-analog in Escherichia coli. AlgR1 is isolated in a phosphorylatable 80-kDa complex in association with AlgR2 in P. aerug inosa and the AlgR2-analog in E. coli.