Genetic suppression analysis of an asgA missense mutation in Myxococcus xanthus

The asgA gene is required for generation of extracellular A signal, which serves as a cell-density signal for fruiting body development in Myxococcus xanthus. The AsgA protein is a histidine protein kinase and consists of a receiver domain that is conserved among response regulators of two-component signal transduction systems, followed by a histidine protein kinase domain that is conserved among sensor proteins of two-component systems. AsgA is thought to function in a signal transduction pathway that leads to expression of genes required for A-signal generation. A genetic suppression analysis of an asgA missense mutation was undertaken in order to identify genes that may provide information regarding the role of AsgA in A-signal generation and fruiting body formation. Twenty-two independent strains containing mutations that suppress asgA473 were isolated by selecting for production of heat-resistant spores under conditions that promote fruiting body development in wild-type cells. Ten of the 22 suppressor strains contained bypass suppressors. All the suppressor strains had direct spore counts at least three to four times greater than the original asgA473 mutant, and three strains had viable counts that exceeded wild-type by more than one order of magnitude. Surprisingly, none of the suppressor strains produced wild-type levels of extracellular A-signal.