COMPLEMENTATION OF SPORULATION AND MOTILITY DEFECTS IN A PROKARYOTE BY A EUKARYOTIC GTPASE

The complex prokaryote, Myxococcus xanthus, undergoes a program of mul ticellular development when starved for nutrients, culminating in spor ulation. M. xanthus makes MglA, a 22-kDa, soluble protein that is requ ired for both multicellular development and gliding motility. MglA is similar in sequence to the Saccharomyces cerevisiae SARI protein, a me mber of the Ras/Rab/Rho superfamily of small eukaryotic GTPases. The S RR1 gene, when integrated into the M. xanthus genome, complements the sporulation defect of a Delta mglA strain. A forward, second-site muta tion on the M. xanthus chromosome, rpm, in combination with SARI, rest ores fruiting body morphogenesis and gliding motility to a Delta mglA strain. The result that the rpm mutation suppresses the substitution o f SAR1 for mglA suggests that Sar1p interacts with other M. xanthus pr oteins to control the motility-dependent aggregation of cells during d evelopment.