PhoR1-PhoP1, a Third Two-Component System of the Family PhoRP from Myxococcus xanthus : Role in Development

The pair PhoR1-PhoP1 is the third two-component system of the family PhoRP reported in M. xanthus. PhoR1 is a histidine kinase anchored to the membrane through a transmembrane domain located in the amino-terminal portion of the protein. As a result, 93% of the protein is located in the cytoplasm. This topology is unusual in the PhoR-type histidine kinases. PhoP1 is a response regulator with a helix-loop-helix motif typical of the DNA-binding proteins. Although the operon phoPR1 is expressed during vegetative growth, it peaks during development. The expression levels of this operon are higher in phosphate-containing media than in those in which the nutrient is absent. A deletion mutant in this system exhibits a delay in aggregation and the formation of fruiting bodies larger than those of the wild-type strain. The expression of the operon is autoregulated. This system is also partially responsible for the expression of Mg-independent acid and neutral phosphatases, but it is not required for the expression of alkaline phosphatases.