Identification of binding sites for the group A streptococcal global regulator CovR

Summary The CovRS two‐component system (also called CsrRS) of the group A streptococcus (GAS) acts as a global regulator, influencing the transcription of at least six virulence factors. The synthesis of the hyaluronic acid capsule, a virulence factor encoded by the hasABC operon, is negatively regulated by CovRS. We confirmed that phosphorylation of CovR increases its binding to a DNA fragment containing the hasA promoter. Using DNase I footprinting, we identified five binding sites surrounding the hasA promoter from bases –79 to + 73 (where + 1 is the start of transcription). One pair of thymines within each binding site appears to be necessary for CovR binding in vitro , as shown by uracil interference analysis. When each of these thymine pairs was altered by site‐directed mutagenesis, CovR binding was reduced in vitro , confirming the role of each thymine pair in binding. Using a transcriptional reporter system with a single chromosomal copy of P hasA–gusA , we demonstrated the importance of each of four of these binding sites for CovR repression of the hasA promoter. Based on this information, we propose a consensus sequence for CovR binding to DNA.