cis Elements necessary for developmental expression of a Myxococcus xanthus gene that depends on C signaling

Cell contact-mediated C signaling coordinates morphogenesis and gene expression during development of Myxococcus xanthus. One promoter that depends on C signaling for transcription lies upstream of Omega4403, the site of a Tn5 lac insertion in the genome. The Omega4403 promoter has a C-box sequence centered at -49 bp that matches the consensus 5'-CAYYCCY-3', which is found in several C-signal-dependent promoters. Mutational analysis of the Omega4403 promoter region was performed to test the importance of the C box and to identify other cis-acting elements. A 6-bp change in the -10 region eliminated promoter activity, but a 6-bp change in the -35 region decreased activity only about twofold. Certain single-base-pair changes in the C box centered at -49 bp abolished promoter activity, establishing the importance of this sequence element. Single-base-pair changes in a C-box-like sequence centered at -77 bp also abolished promoter activity, but the pattern of mutational effects was different from that for the C box centered at -49 bp. Additional single-base-pair changes indicated that all 10 bp from -79 to -70 bp are important for Omega4403 promoter activity. Mutations at -59, -61, -62, and -63 bp also abolished promoter activity, defining a 5-bp element from -63 to -59 bp. This 5-bp element is separated from the 10-bp element (i.e., -79 to -70 bp) by 6 bp that can be changed without loss of promoter activity. Likewise, the 5 bp between the 5-bp element and the C box can be changed without loss of activity, but deletion of these 5 bp abolished activity, indicating that spacing is important. Sequences similar to the 5- and 10-bp elements, as well as the C box, are present in other C-signal-dependent promoters, suggesting some similarity in the regulatory mechanisms, but there are also indications that these cis elements do not function identically in the different promoters.