title: CovR alleviates transcriptional silencing by a nucleoid-associated histone-like protein in Streptococcus mutans.
abstract: In Streptococcus mutans, the global response regulator CovR plays an important role in biofilm formation, stress tolerance response, and caries production. We have previously demonstrated that CovR activates a large gene cluster, which is a part of a genomic island, TnSmu2. In this article, we have further characterized CovR at the molecular level to understand the gene activation mechanism. Toward this end, we mapped the transcription start site of the operon that lies upstream of the SMU.1348 gene (P(SMU.1348)), the first gene of the cluster. We constructed a transcriptional reporter fusion and showed that CovR induces expression from P(SMU.1348). We also demonstrated that purified CovR protects the sequence surrounding the -10 region of P(SMU.1348). In an in vitro transcription assay, we showed that histone-like protein (HLP), a homologue of Escherichia coli HU protein, represses transcription from P(SMU.1348). In vivo overexpression of HLP in trans also represses transcription from P(SMU.1348). Addition of CovR to the HLP-repressed P(SMU.1348) resulted in increased transcription from the promoter, suggesting a role for CovR in countering HLP silencing. Moreover, addition of SMU.1349, a transcriptional activator of the operon, to the in vitro assay further stimulated the transcription. Based on our in vivo and in vitro results, we propose a model for transcriptional activation of the operon.
authors.affiliation: Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, Kansas, USA. ibiswas@kumc.edu
authors.forename: Indranil
authors.initials: I
authors.lastname: Biswas
authors.forename: Saswat Sourav
authors.initials: SS
authors.lastname: Mohapatra
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D020868:Gene Silencing; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013295:Streptococcus mutans / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; C040330:histone-like protein HU, bacteria