IDENTIFICATION OF THE OMEGA-4400 REGULATORY REGION, A DEVELOPMENTAL PROMOTER OF MYXOCOCCUS-XANTHUS

Omega 4400 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 normal expression of Tn5 lac Omega 4400 . The DNA upstream of the Omega 4400 insertion has been cloned, the pr omoter has been localized, and a partial open reading frame has been i dentified. From the deduced amino acid sequence of the partial open re ading frame, the gene disrupted by Tn5 lac Omega 4400 may encode a pro tein with an ATP-or GTP-binding site. Expression of the gene begins 6 to 12 h after starvation initiates development, as measured by P-galac tosidase production in cells containing Tn5 be Omega 4400. The putativ e transcriptional start site was mapped, and deletion analysis has sho wn that DNA downstream of -101 bp is sufficient for C-signal-dependent , developmental activation of this promoter. A deletion to -76 bp elim inated promoter activity, suggesting the involvement of an upstream ac tivator protein. The promoter may be transcribed by RNA polymerase con taining a novel sigma factor, since a mutation in the M. xanthus sigB or sigC gene did not affect Tn5 lac Omega 4400 expression and the DNA sequence upstream of the transcriptional start site did not match the sequence of any M. xanthus promoter transcribed by a known form of RNA polymerase, However, the Omega 4400 promoter does contain the sequenc e 5'-CATCCCT-3' centered at -49 and the C-signal-dependent Omega 4403 promoter also contains this sequence at the same position. Moreover, t he two promoters match at five of six positions in the -10 regions, su ggesting that these promoters may share one or more transcription fact ors. These results begin to define the cis-acting regulatory elements important for cell-cell interaction-dependent gene expression during t he development of a multicellular prokaryote.