SUPPRESSION OF A SIGNALING DEFECT DURING MYXOCOCCUS-XANTHUS DEVELOPMENT

The csgA gene encodes an extracellular protein that is essential for c ell-cell communication (C-signaling) during fruiting body development of Myxococcus xanthus. Two transposon insertions in the socABC operon, sec-560 and socC559, restore development to csgA null mutants, Mixing sec-560 csgA cells or socC559 csgA cells with csgA cells at a ratio o f 1:1 stimulated the development of csgA cells, suggesting that soc mu tations allow. cells to produce the C-signal or a similar molecule via a csgA-independent mechanism. The socABC operon contains the followin g three genes: socA, a member of the short-chain alcohol dehydrogenase gene family; socB, a gene encoding a putative membrane anchoring prot ein; and socC, a negative autoregulator of socABC operon expression, B oth suppressor mutations inactivate socC, leading to a 30- to 100-fold increase in socA transcription; socA expression in suppressor strains is at least 100-fold higher than csgA expression during all stages of development, The amino acid sequence of SocA has 28% identity and 51% similarity with that of CsgA, We suggest that CsgA suppression is due to overproduction of SocA, which can substitute for CsgA, These resul ts raise the possibility that a cell surface dehydrogenase plays a rol e in C-signaling.