CorE from Myxococcus xanthus Is a Copper-Dependent RNA Polymerase Sigma Factor

Abstract

The dual toxicity/essentiality of copper forces cells to maintain a tightly regulated homeostasis for this metal in all living organisms, from bacteria to humans. Consequently, many genes have previously been reported to participate in copper detoxification in bacteria. Myxococcus xanthus, a prokaryote, encodes many proteins involved in copper homeostasis that are differentially regulated by this metal. A σ factor of the ECF (extracytoplasmic function) family, CorE, has been found to regulate the expression of the multicopper oxidase cuoB, the P1B-type ATPases copA and copB, and a gene encoding a protein with a heavy-metal-associated domain. Characterization of CorE has revealed that it requires copper to bind DNA in vitro. Genes regulated by CorE exhibit a characteristic expression profile, with a peak at 2 h after copper addition. Expression rapidly decreases thereafter to basal levels, although the metal is still present in the medium, indicating that the activity of CorE is modulated by a process of activation and inactivation. The use of monovalent and divalent metals to mimic Cu(I) and Cu(II), respectively, and of additives that favor the formation of the two redox states of this metal, has revealed that CorE is activated by Cu(II) and inactivated by Cu(I). The activation/inactivation properties of CorE reside in a Cys-rich domain located at the C terminus of the protein. Point mutations at these residues have allowed the identification of several Cys involved in the activation and inactivation of CorE. Based on these data, along with comparative genomic studies, a new group of ECF σ factors is proposed, which not only clearly differs mechanistically from the other σ factors so far characterized, but also from other metal regulators.

Two Systems for Conditional Gene Expression in Myxococcus xanthus Inducible by Isopropyl-β- d -Thiogalactopyranoside or Vanillate

“…The system works well for copper at Յ0.5 mM during vegetative growth and at Յ0.06 mM for fruiting body formation, but higher copper levels affect cell growth and fruiting body development, while even small amounts of copper can interfere somewhat with social and adventurous motility (14). Moreover, besides toxicity, other issues concerning the use of copper to control expression of genes include collateral effects on cell physiology due to induction of other genes, such as those for copper homeostasis and carotenogenesis (13,31).…”

Transcriptional and Posttranscriptional Events Control Copper-Responsive Expression of a Rhodobacter capsulatus Multicopper Oxidase

“…CueR acts as a single protein consisting of two domains, a DNA-binding domain and a copper-binding domain, with the latter sensing the cytoplasmic copper status. Recently, a copper-dependent extracytoplasmic function (ECF) sigma factor was shown to activate P-type ATPase and multicopper oxidase genes in Myxococcus xanthus (14). In Gram-positive bacteria, copper defense genes are mostly repressed by CsoR or CopY regulators at low copper concentrations (23,44).…”

Dual Positive Feedback Regulation of Protein Degradation of an Extra-cytoplasmic Function σ Factor for Cell Differentiation in Streptomyces coelicolor

“…6C), further supporting the idea that SigT can solely bind to clpPp. The binding of factors to promoters without core enzymes has also been in evidence in studies of several other factors, such as CorE in Myxococcus xanthus (38), SigA from Bacillus subtilis (39), and Tt-RpoE1 from Thermoanaerobacter tengcongensis (40). Furthermore, two binding sites of SigT on clpPp were determined by a DNase I footprinting assay (Fig.…”