Phosphorylation at the D53 but Not the T65 Residue of CovR Determines the Repression of and Transcription in 1- and 49-Type Group A Streptococci.

CovR/CovS is a two-component regulatory system in group A and primarily acts as a transcriptional repressor. The D53 residue of CovR (CovR) is phosphorylated by the sensor kinase CovS, and the phosphorylated CovR protein binds to the intergenic region of to inhibit transcription. Nonetheless, the transcription of and is suppressed in mutants. The T65 residue of CovR is phosphorylated in a CovS-independent manner, and phosphorylation at the D53 and T65 residues of CovR is mutually exclusive. Therefore, how phosphorylation at the D53 and T65 residues of CovR contributes to the regulation of and expression was elucidated. The transcription of and was suppressed in the strain that cannot phosphorylate the D53 residue of CovR (CovR mutant) but restored to levels similar to those of the wild-type strain in the CovR mutant. Nonetheless, inactivation of the T65 residue phosphorylation in the CovR mutant cannot derepress the and transcription, indicating that phosphorylation at the T65 residue of CovR is not required for repressing and transcription. Furthermore, complementation of the CovR protein in the strain that expresses the phosphorylated CovR resulted in the repression of and transcription. Unlike the direct binding of the phosphorylated CovR protein and its inhibition of transcription demonstrated previously, the present study showed that inactivation of phosphorylation at the D53 residue of CovR contributes dominantly in suppressing and transcription. CovR/CovS is a two-component regulatory system in group A (GAS). The D53 residue of CovR is phosphorylated by CovS, and the phosphorylated CovR binds to the intergenic region and acts as the transcriptional repressor. Nonetheless, the transcription of and Rgg-controlled is upregulated in the mutant but inhibited in the mutant. The present study showed that nonphosphorylated CovR protein inhibits and transcription in the presence of the phosphorylated CovR, indicating that nonphosphorylated CovR has a dominant role in suppressing transcription. These results reveal the roles of nonphosphorylated CovR in regulating transcription, which could contribute significantly to invasive phenotypes of mutants.