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The N terminus of Myxococcus xanthus CarA repressor is an autonomously folding domain that mediates physical and functional interactions with both operator DNA and antirepressor protein

AuthorsPérez-Marín, Mari Cruz; López-Rubio, Jose Juan; Murillo, Francisco J.; Elías-Arnanz, Montserrat; Padmanabhan, Subramanian CSIC ORCID
Issue Date25-May-2004
PublisherAmerican Society for Biochemistry and Molecular Biology
CitationJournal of Biological Chemistry 279(32): 33093-33103 (2004)
AbstractExpression of the Myxococcus xanthus carB operon, which encodes the majority of the enzymes involved in light-induced carotenogenesis, is down-regulated in the dark by the CarA repressor binding to its bipartite operator. CarS, produced on illumination, relieves repression of carB by physically interacting with CarA to dis-mantle CarA-DNA complexes. Here, we demonstrate that the N- and C-terminal portions of CarA are organized as distinct structural and functional domains. Specifically, we show that the 78 N-terminal residues of CarA, CarA(Nter), form a monomeric, highly helical, autonomously folding unit with significant structural stability. Significantly, CarA(Nter) houses both the operator and CarS binding specificity determinants of CarA. CarA(Nter) binds operator with a lower affinity than whole CarA, and the CarA(Nter)-CarS complex has a 1:1 stoichiometry. In vitro, sufficiently high concentrations of CarA(Nter) block M. xanthus RNA polymerase-promoter binding, and this is relieved by CarS. In vivo, substitution of the gene carA by that for CarA(Nter) results in constitutive expression of carB just as in a carA-deleted background. However, re-engineering the latter strain to overexpress CarA(Nter) restores repression of carB. Thus, the 78-residue N-terminal portion of CarA is an autonomously folded, dual function domain that orchestrates specific DNA-protein and protein-protein interactions and, when overexpressed, can be functionally competent in vivo.
Description11 pages, 9 figures, 1 table.-- PMID: 15163666 [PubMed].-- Printed version published Aug 6, 2004.-- Full-text version available Open Access at the journal site.
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