VP963/DK1622

Phosphate regulation is complex in the developmental prokaryote Myxococcus xanthus, and requires at least three previously characterized two-component systems (TCS), designated PhoR1-PhoP1, PhoR2-PhoP2, and PhoR3-PhoP3. We report here the identification and characterization of a member of a fourth TCS, designated PhoP4, which shows high sequence similarity to the other three M. xanthus PhoP response regulators. PhoP4 is an orphan response regulator that was identified by yeast 2-hybrid screen as a possible interacting partner of PhoR2. phoP4 insertion mutation and in-frame deletion strains were constructed and assessed for developmental and phosphatase phenotypes, and then compared with the phenotypes previously reported for a _phoR2-phoP2 strain. The data indicate that the phoP4 mutations caused spore viability to be decreased by nearly two orders of magnitude, and reduced all three development-specific phosphatase activities by 80-90% under phosphate-limiting conditions. These phenotypes are stronger than those observed for mutations in the PhoR2-PhoP2 system, thereby suggesting a high degree of complexity vis-à-vis the interactions amongst the Pho signal transduction pathways in M. xanthus. Keywords: developmental analysis 3 biological replicates with 3 time points each, normalized ratios to Cy3