Open AccessRegulation of ciaXRH Operon Expression and Identification of the CiaR Regulon in Streptococcus mutans
Author(s) -
Chenggang Wu,
Eduardo A. Ayala,
Jennifer S. Downey,
Justin Merritt,
Steven D. Goodman,
Fengxia Qi
Publication year - 2010
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.00556-10
Subject(s) - regulon , biology , operon , genetics , mutant , gene , promoter , phenotype , regulation of gene expression , transcriptional regulation , wild type , microbiology and biotechnology , gene expression
TheciaRH operon inStreptococcus mutans contains 3 contiguous genes,ciaXRH . Unlike the CiaRH system in other streptococci, only theciaH -null mutant displays defective phenotypes, while theciaR -null mutant behaves like the wild type. The objective of this study was to determine the mechanism of this unusual property. We demonstrate that theciaH mutation caused a >20-fold increase inciaR transcript synthesis. AciaRH double deletion reversed theciaH phenotype, suggesting that overexpressedciaR might be responsible for the observedciaH phenotypes. WhenciaR was forced to be overexpressed by a transcriptional fusion to theldh promoter in the wild-type background, the sameciaH phenotypes were restored, confirming the involvement of overexpressedciaR in theciaH phenotypes. TheciaH mutation andciaR overexpression also caused transcriptional alterations in 100 genes, with 15 genes upregulated >5-fold. Bioinformatics analysis identified a putative CiaR regulon consisting of 8 genes/operons, including theciaXRH operon itself, all of which were upregulated.In vitro footprinting on 4 of the 8 promoters revealed a protected region of 26 to 28 bp encompassing two direct repeats, NTTAAG-n5-WTTAAG, 10 bp upstream of the −10 region, indicating direct binding of the CiaR protein to these promoters. Taken together, we conclude that overexpressed CiaR, as a result of eitherciaH deletion or forced expression from a constitutive promoter, is a mediator in the CiaH-regulated phenotypes.