title: Regulation of competence and gene expression in Streptococcus mutans by the RcrR transcriptional regulator.
abstract: An intimate linkage between the regulation of biofilm formation, stress tolerance and genetic competence exists in the dental caries pathogen Streptococcus mutans. The rcrRPQ genes encode ABC exporters (RcrPQ) and a MarR-family transcriptional repressor of the rcr operon (RcrR) that play a dominant role in the regulation of the development of genetic competence and connect competence with stress tolerance and (p)ppGpp production in S. mutans. Here we identify the target for efficient RcrR binding in the rcr promoter region using purified recombinant RcrR (rRcrR) protein in electrophoretic mobility shift assays and show that DNA fragments carrying mutations in the binding region were not bound as efficiently by rRcrR in vitro. Mutations in the RcrR binding site impacted expression from the rcrR promoter in vivo and elicited changes in transformation efficiency, competence gene expression, and growth inhibition by competence-stimulating peptide; even when the changes in rcrRPQ transcription were minor. An additional mechanistic linkage of RcrR with competence and (p)ppGpp metabolism was identified by showing that the rRcrR protein could bind to the promoter regions of comX, comYA and relP, although the binding was not as efficient as to the rcrRPQ promoter under the conditions tested. Hence, tightly controlled autogenous regulation of the rcrRPQ operon by RcrR binding to specific target sites is essential for cellular homeostasis, and RcrR contributes to the integration of genetic competence, (p)ppGpp metabolism, and acid and oxidative stress tolerance in S. mutans through both direct and indirect mechanisms.
authors.affiliation: Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610.
authors.forename: Kinda
authors.initials: K
authors.lastname: Seaton
authors.affiliation: Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610.
authors.forename: Sang-Joon
authors.initials: SJ
authors.lastname: Ahn
authors.affiliation: Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Burne
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001665:Binding Sites; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D009876:Operon; D011401:Promoter Regions, Genetic; D013295:Streptococcus mutans / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins
keywords: autolysis; dental caries; genetic competence; peptide signalling; transcriptional regulator