CHARACTERIZATION OF THE REGULATORY REGION OF A CELL INTERACTION-DEPENDENT GENE IN MYXOCOCCUS-XANTHUS

Omega 4403 is the site of a Tn5 lac insertion in the Myxococcus xanthu s genome that fuses lacZ expression to a developmentally regulated pro moter. Cell-cell interactions that occur during development, including C-signaling, are required for expression of Tn5 lac Omega 4403. We ha ve cloned DNA upstream of the Omega 4403 insertion site, localized the promoter, and identified a potential open reading frame. From the ded uced amino acid sequence, the gene disrupted by Tn5 lac Omega 4403 app ears to encode a serine protease that is dispensable for development. The gene begins to be expressed between 6 and 12 h after starvation in itiates development, as determined by measuring mRNA or beta-galactosi dase accumulation in cells containing Tn5 lac Omega 4403. The putative transcriptional start site was mapped, and sequences centered near -1 0 and -35 bp relative to this site show some similarity-to the corresp onding regions of promoters transcribed by Escherichia coli sigma(70) RNA polymerase. However; deletions showed that an essential promoter e lement lies between -80 and -72 bp, suggesting the possible involvemen t of an upstream activator protein. DNA downstream of -80 is sufficien t for C-signal-dependent activation of this promoter. The promoter is not fully expressed when fusions are integrated at the Mx8 phage attac hment site in the chromosome. Titration of a limiting factor by two co pies of the regulatory region (one at the attachment site and one at t he native site) can, in part, explain the reduced expression. We specu late that the remaining difference may be due to an effect of chromoso mal position. These results provide a basis for studies aimed at ident ifying regulators of C-signal-dependent gene expression.