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

Abstract

Upon starvation, a dense population of rod-shaped Myxococcus xanthus bacteria coordinate their movements to construct mounds in which some of the cells differentiate to spherical spores. During this process of fruiting body formation, short-range C-signaling between cells regulates their movements and the expression of genes important for sporulation. C-signaling activates FruA, a transcription factor that binds cooperatively with another transcription factor, MrpC2, upstream of the fmgA and fmgBC promoters, activating transcription. We have found that a third C-signal-dependent gene, herein named fmgD, is subject to combinatorial control by FruA and MrpC2. The two proteins appear to bind cooperatively upstream of the fmgD promoter and activate transcription. FruA binds proximal to the fmgD promoter, as in the fmgBC promoter region, whereas MrpC2 binds proximal to the fmgA promoter. A novel feature of the fmgD promoter region is the presence of a second MrpC2 binding site partially overlapping the promoter and therefore likely to mediate repression. The downstream MrpC2 site appears to overlap the FruA site, so the two transcription factors may compete for binding, which in both cases appears to be cooperative with MrpC2 at the upstream site. We propose that binding of MrpC2 to the downstream site represses fmgD transcription until C-signaling causes the concentration of active FruA to increase sufficiently to outcompete the downstream MrpC2 for cooperative binding with the upstream MrpC2. This would explain why fmgD transcription begins later during development and is more dependent on C-signaling than transcription of fmgA and fmgBC.

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

“…In each case, binding of the two proteins cooperatively to a site located immediately upstream of the promoter appears to activate transcription. However, insertion mutations in these genes cause, at most, mild defects in fruiting body formation (34,(39)(40)(41). In contrast, insertions in the dev operon impair sporulation dramatically (3,5).…”

“…MrpC2 binds cooperatively with FruA to the promoter regions of several C-signal-dependent genes in vitro (34,(39)(40)(41). Mutations in the cooperative binding sites affect promoter activity in vivo.…”

“…The expression of several C-signal-dependent genes has been shown to be under the combinatorial control of FruA and MrpC2 (34,(39)(40)(41). MrpC2 is an N-terminally truncated form of MrpC (42), a protein similar to transcription factors in the cyclic AMP receptor protein (CRP) family (43).…”

Myxococcus xanthus Developmental Cell Fate Production: Heterogeneous Accumulation of Developmental Regulatory Proteins and Reexamination of the Role of MazF in Developmental Lysis

“…Increased activation of FruA is proposed to induce FruA-dependent transcription of several target genes. In many cases, FruA acts in combination with MrpC2 (22,33,34,55). One important target of FruA/MrpC2 is the dev locus (62), which is expressed at high levels in aggregation centers (16), is necessary for efficient sporulation (59), and additionally promotes upregulation of fruA, inducing a positive-feedback loop (7).…”

The dev Operon Regulates the Timing of Sporulation during Myxococcus xanthus Development

“…Since the transcription of fruA depends on MrpC (15), and the two transcription factors bind DNA promoter regions cooperatively to regulate the transcription of many genes (16)(17)(18)(19)(20), including the dev operon (9), we also measured the MrpC level during development of the ΔdevT mutants. Consistent with an earlier blockage of the developmental program in the original ΔdevT408 -502 mutant, MrpC accumulation was reduced relative to wild-type DK1622 (Fig.…”