Combinatorial Regulation of thedevOperon by MrpC2 and FruA during Myxococcus xanthus Development

Abstract

Proper expression of thedevoperon is important for normal development ofMyxococcus xanthus. When starved, these bacteria coordinate their gliding movements to build mounds that become fruiting bodies as some cells differentiate into spores. Mutations in thedevTRSgenes impair sporulation. Expression of the operon occurs within nascent fruiting bodies and depends in part on C signaling. Here, we report that expression of thedevoperon, like that of several other C-signal-dependent genes, is subject to combinatorial control by the transcription factors MrpC2 and FruA. A DNA fragment upstream of thedevpromoter was bound by a protein in an extract containing MrpC2, protecting the region spanning positions −77 to −54. Mutations in this region impaired binding of purified MrpC2 and abolished developmental expression of reporter fusions. The association of MrpC2 and/or its longer form, MrpC, with thedevpromoter region depended on FruAin vivo, based on chromatin immunoprecipitation analysis, and purified FruA appeared to bind cooperatively with MrpC2 to DNA just upstream of thedevpromoterin vitro. We conclude that cooperative binding of the two proteins to this promoter-proximal site is crucial fordevexpression. 5′ deletion analysis implied a second upstream positive regulatory site, which corresponded to a site of weak cooperative binding of MrpC2 and FruA and boosteddevexpression 24 h into development. This site is unique among the C-signal-dependent genes studied so far. Deletion of this site in theM. xanthuschromosome did not impair sporulation under laboratory conditions.