MrpC, a CRP/Fnr homolog, functions as a negative autoregulator during the Myxococcus xanthus multicellular developmental program

Abstract

MrpC, a member of the CRP/Fnr superfamily of transcriptional regulators, plays a key role in coordination of the multicellular developmental program in Myxococcus xanthus. Previous reports suggest MrpC is subject to complex regulation including activation by an unusual LonD-dependent proteolytic processing event that removes its unique N-terminal peptide, producing the isoform MrpC2. MrpC2 is proposed to positively autoregulate and regulate transcription of hundreds of genes necessary for both the aggregation and sporulation phases of the developmental program. We demonstrate here that mrpC expression bifurcates corresponding to different cell populations within the developmental program. During our analysis of regulatory events controlling this process, we demonstrate that MrpC2 is not an active isoform; rather, the N-terminal peptide is instead essential for MrpC function in vivo. We also demonstrate that MrpC is instead a negative autoregulator and represses its own expression by specifically competing with its enhancer binding protein, MrpB. These results provide an additional rare example of CRP / EBP coordinated regulation, and significantly revise the model for control of the central developmental transcriptional activator of the M. xanthus developmental program. This article is protected by copyright. All rights reserved.

A negative autoregulation network motif is required for synchronizedMyxococcus xanthusdevelopment

“…mrpC expression is subject to NAR due at least in part to competition between MrpC and its transcriptional activator, MrpB, for overlapping binding sites (21) (Fig. S1A).…”

“…MrpC binds to two additional sequences within its promoter (termed BS5 and BS1; Fig. S1A) (21). To examine whether BS5 and BS1 contributed to MrpC NAR, we analyzed mrpC expression reporter constructs bearing the wild type promoter or mutant promoters bearing perturbation of BS1 (BS1*), deletion of BS5 (ΔBS5), or both (ΔBS5 BS1*).…”

“…To examine whether BS5 and BS1 contributed to MrpC NAR, we analyzed mrpC expression reporter constructs bearing the wild type promoter or mutant promoters bearing perturbation of BS1 (BS1*), deletion of BS5 (ΔBS5), or both (ΔBS5 BS1*). BS1* was generated by substituting the TGT consensus resides to GAA which completely disrupts MrpC binding to BS1 in vitro (21)(Fig. S1B).…”

“…Shortly after cells sense nutrient limitation, mrpC expression is upregulated by MrpB, a bacterial enhancer binding protein (bEBP) (16). MrpB binds to two upstream activating sequences (UAS1 and UAS2) 182 bp from the mrpC start codon and is proposed to stimulate mrpC expression from a sigma 54 -dependent promoter (16, 21). Early during the developmental program, gradual accumulation of MrpC is achieved because the Esp signaling system induces turnover of MrpC (22, 23).…”

“…A long-standing model suggested MrpC acted as positive autoregulator, leading to the attractive speculation that bifurcation of MrpC production (a known feature of positive autoregulation motifs (25)) could drive cell fate segregation into either aggregation centers or peripheral rods [summarized in (15)]. Recently, however, we demonstrated that MrpC functions instead as a negative autoregulator by competing with its transcriptional activator, MrpB, for overlapping binding sites in the mrpC promoter region (21).…”