A-signaling plays an essential role in the early stages of Myxococcus xanthus fruiting body development. Expression of the 452I gene, which is regulated at the level of RNA accumulation, depends on starvation and on A-signaling. To identify the cis-acting regulatory elements which 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 bases which were conserved between the sigma 54 consensus, mbhA, and 4521 promoters were also important for 4521 promoter activity. Changes which altered the spacing between two conserved regions centered around positions -14 and -24 abolished promoter activity. In contrast, mutations 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 respect to timing of expression and requirement for a solid surface and extracellular signals. This suggests a model in which different activator proteins may be responsible for regulating expression of these two genes
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