The CarD/CarG regulatory complex is required for the action of several members of the large set of Myxococcus xanthus extracytoplasmic function σ factors

Abstract

Extracytoplasmic function (ECF) σ factors are critical players in signal transduction networks involved in bacterial response to environmental changes. The Myxococcus xanthus genome reveals ∼45 putative ECF-σ factors, but for the overwhelming majority, the specific signals or mechanisms for selective activation and regulation remain unknown. One well-studied ECF-σ, CarQ, binds to its anti-σ, CarR, and is inactive in the dark but drives its own expression from promoter P(QRS) on illumination. This requires the CarD/CarG complex, the integration host factor (IHF) and a specific CarD-binding site upstream of P(QRS). Here, we show that DdvS, a previously uncharacterized ECF-σ, activates its own expression in a CarD/CarG-dependent manner but is inhibited when specifically bound to the N-terminal zinc-binding anti-σ domain of its cognate anti-σ, DdvA. Interestingly, we find that the autoregulatory action of 11 other ECF-σ factors studied here depends totally or partially on CarD/CarG but not IHF. In silico analysis revealed possible CarD-binding sites that may be involved in direct regulation by CarD/CarG of target promoter activity. CarD/CarG-linked ECF-σ regulation likely recurs in other myxobacteria with CarD/CarG orthologous pairs and could underlie, at least in part, the global regulatory effect of the complex on M. xanthus gene expression.

Metal‐responsive RNA polymerase extracytoplasmic function (ECF) sigma factors

“…Instead, CarG interacts with the N‐terminal domain of CarD to function as a transcriptional regulatory unit (Peñalver‐Mellado et al , ). Interestingly, the CarD‐CarG complex is also required for proper activity by other M. xanthus ECF sigma factors, none of which are known to respond to metals (Abellón‐Ruiz et al , ).…”

Highly Signal-Responsive Gene Regulatory Network Governing Myxococcus Development

“…In the Streptomyces GRN, mixed cascades of σ factors and other transcription factors play the dominant role, with modulation of the activity of some σ factors by anti-σ factors [78, 80]. In contrast, very little is known about involvement of σ and anti-σ factors in the Myxococcus GRN, except that EBPs presumably activate transcription by σ 54 RNA polymerase and that the genome encodes 52 σ factors in the σ 70 family and at least 30 anti-σ factors [83, 84]. These potential components of the developmental GRN present intriguing opportunities for future exploration.…”

The predatory life cycle of Myxococcus xanthus

“…xanthus focused on the motility, cell-signalling and morphogenesis of Myx. xanthus into fruiting bodies Sun et al, 2000;Abelló n-Ruiz et al, 2014;Huntley et al, 2011).…”