AN EARLY A-SIGNAL-DEPENDENT GENE IN MYXOCOCCUS-XANTHUS HAS A SIGMA(54)-LIKE PROMOTER

A-signaling plays an essential role in the early stages of Myxococcus xanthus fruiting body development, Expression of the 4521 gene, which is regulated at the level of RNA accumulation, depends on starvation a nd on A-signaling, To identify the cis-acting regulatory elements whic h allow gene 4521 to respond to the nutritional and A-factor signals, the 4521 transcription start site was mapped, The region just upstream of the start site showed sequence similarity to the sigma(54) family of promoters and to the developmentally regulated mbhA promoter of M, xanthus, A mutational analysis of this region established that the bas es which were conserved between the sigma(54) consensus, mbhA, and 452 1 promoters were also important for 4521 promoter activity, Changes wh ich altered the spacing between two conserved regions centered around positions -14 and -24 abolished promoter activity, In contrast, mutati ons in a putative -10 region for a sigma(70)-like promoter had little effect on expression of 4521, Despite their similar promoter regions, the regulation of the 4521 and mbhA genes was shown to differ with res pect to timing of expression and requirement for a solid surface and e xtracellular signals, This suggests a model in which different activat or proteins may be responsible for regulating expression of these two genes.