Complementation of sporulation and motility defects in a prokaryote by a eukaryotic GTPase

The complex prokaryote, Myxococcus xanthus, undergoes a program of multicellular development when starved for nutrients, culminating in sporulation. M. xanthus makes MglA, a 22-kDa, soluble protein that is required for both multicellular development and gliding motility. MglA is similar in sequence to the Saccharomyces cerevisiae SARI protein, a member of the Ras/Rab/Rho superfamily of small eukaryotic GTPases. The SRR1 gene, when integrated into the M. xanthus genome, complements the sporulation defect of a Delta mglA strain. A forward, second-site mutation on the M. xanthus chromosome, rpm, in combination with SARI, restores fruiting body morphogenesis and gliding motility to a Delta mglA strain. The result that the rpm mutation suppresses the substitution of SAR1 for mglA suggests that Sar1p interacts with other M. xanthus proteins to control the motility-dependent aggregation of cells during development.