title: Characterization of irvR, a novel regulator of the irvA-dependent pathway required for genetic competence and dextran-dependent aggregation in Streptococcus mutans.
abstract: Previous studies identified irvA as a normally repressed but highly inducible transcription regulator capable of repressing mutacin I gene expression in Streptococcus mutans. In this study, we aimed to identify and characterize the regulator(s) responsible for repressing the expression of irvA. An uncharacterized open reading frame (SMU.1398) located immediately adjacent to irvA and annotated as a putative transcription repressor was identified as a likely candidate. The results of mutation studies confirmed that the expression of irvA was greatly increased in the SMU.1398 background. Mutation of SMU.1398 ("irvR") abolished genetic competence and reduced the expression of the late competence genes/operons comEA, comY, and dprA without affecting the expression of the known competence regulators comC, comED, or comX. In addition, irvR was found to be a potent negative regulator of dextran-dependent aggregation (DDAG) and gbpC expression. Each of these irvR mutant phenotypes could be rescued with a double mutation of irvA or complemented by introducing a wild-type copy of irvR on a shuttle vector. These data indicate that the repression of irvA is critically dependent upon irvR and that irvA repression is essential for the development of genetic competence and the proper control of DDAG in S. mutans.
authors.affiliation: Department of Oral Biology, College of Dentistry, University of Oklahoma Health Sciences Center BRC364, 975 NE 10th St., Oklahoma City, OK 73104-5419, USA.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Niu
authors.forename: Toshinori
authors.initials: T
authors.lastname: Okinaga
authors.forename: Lin
authors.initials: L
authors.lastname: Zhu
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Banas
authors.forename: Felicia
authors.initials: F
authors.lastname: Qi
authors.forename: Justin
authors.initials: J
authors.lastname: Merritt