Identification of the Omega 4499 regulatory region controlling developmental expression of a Myxococcus xanthus cytochrome P-450 system

Omega 4499 is the site of a Tn5 lac insertion in the Myxococcus xanthus chr omosome that fuses lacZ expression to a developmentally regulated promoter. Cell cell interactions that occur during development, including C signalin g, are required for normal expression of Tn5 lac Omega 4499. The DNA upstre am of the Omega 4499 insertion has been cloned, and the promoter has been l ocalized. Analysis of the DNA sequence downstream of the promoter revealed one complete open reading frame and a second partial open reading frame tha t is interrupted by Tn5 lac Omega 4499. The predicted products of these ope n reading frames are highly similar to reductase and oxidase components of bacterial cytochrome P-450 systems, which allow catabolism or anabolism of unusual compounds. However, the function of the gene products of the Omega 4499 locus remains unclear because M. xanthus containing Tn5 lac Omega 4499 exhibits no apparent defect in growth, developmental aggregation, fruiting body formation, or sporulation. Deletion analysis of the Omega 4499 regula tory region showed that multiple DNA elements spanning more than 500 bp ups tream of the transcriptional start site contribute to developmental promote r activity. At least two DNA elements, one downstream of -49 bp and one bet ween -49 and -218 bp, boosted activity of the promoter in response to inter cellular C signaling. Three sequences in the Omega 4499 promoter region, ce ntered at -55, -33, and -1 bp, nearly match a 7-bp sequence found in other C signal-dependent promoters. We propose that these sequences, matching the consensus sequence 5'-CAYYCCY-3', be called C box sequences, and we specul ate that these sequences are cis-acting regulatory elements important for t he expression of M. xanthus genes that depend upon intercellular C signalin g during development.