Hyperphosphorylation of the Group A Streptococcal Control of Virulence Regulator Increases Promoter Occupancy Specifically at Virulence Factor Encoding Genes
The control of virulence two-component gene regulatory system (CovRS) is critical to the pathogenesis of many medically important streptococci.  In emm1 group A streptococci (GAS), CovR directly binds the promoters of numerous GAS virulence factor encoding genes. Elimination of CovS phosphatase activity increases CovR phosphorylation (CovR~P) levels and abrogates GAS virulence. Given the emm type-specific diversity of CovRS function, herein we used ChIP-seq to define global CovR DNA occupancy in the wild-type emm3 strain MGAS10870 (medium CovR~P) and its CovS phosphatase-negative derivative 10870-CovS-T284A (high CovR~P).  In the wild-type emm3 strain, 89% of the previously identified emm1 CovR binding sites present in the emm3 genome were also enriched; additionally, we ascertained unique CovR binding, primarily to genes in mobile genetic elements and other sites of inter-strain chromosomal differences.  Elimination of phosphatase activity specifically increased CovR occupancy at the promoters of a broad array of CovR repressed virulence factor encoding genes, including those encoding the key GAS regulator Mga and M protein.  However, a limited number of promoters had augmented enrichment at low CovR~P levels. Differential motif searches using sequences enriched at high vs. low CovR~P levels revealed two distinct binding patterns. At high CovR~P, a pseudo-palindromic AT-rich consensus sequence consistent with CovR binding as a dimer was determined.  Conversely, sequences specifically enriched at low CovR~P contained isolated “ATTARA” motifs suggesting an interaction with a monomer.  These data extend understanding of global CovR DNA occupancy beyond emm1 GAS and provide a mechanism for previous observations regarding hypovirulence induced by CovS phosphatase abrogation. Overall design: ChIP-seq analysis using anti-CovR antibody of wild-type (MGAS10870) and high phosphorylation (10870-CovS-T284A) strains