RR06 activates transcription of spr1996 and cbpA in Streptococcus pneumoniae.

Streptococcus pneumoniae colonizes at the nasopharynx of humans and is able to disseminate and cause various infections. The hallmark of pneumococcal disease is rapid bacterial replication in different tissue sites leading to intense inflammation. The genetic basis of pneumococcal adaptation to different host niches remains sketchy. In this study, we investigated the regulatory effect of RR06, a response regulator protein, on gene expression of S. pneumoniae. Microarray and Northern blot analyses showed that RR06 is specifically required for transcription of spr1996 and cbpA. While the function of Spr1996 is unknown, CbpA has been well characterized as a surface-exposed protective antigen and a virulence factor of S. pneumoniae. A recombinant form of RR06 was able to bind to a 19-bp conserved sequence shared by the spr1996 and cbpA promoter regions. Furthermore, inactivation of rr06 resulted in loss of CbpA expression as detected by antibody staining and bacterial adhesion. CbpA expression was restored in trans by the intact rr06 gene. However, a mutant, RR06(D51A), with a point mutation in the aspartate residue at position 51 (a predicted major phosphorylation site) of RR06, completely abolished the CbpA expression, suggesting that RR06 phosphorylation is required for transcriptional activation of spr1996 and cbpA. Finally, inactivation of rr06 in additional pneumococcal strains also led to the loss of CbpA expression. These data implicate that RR06 activates the expression of spr1996 and cbpA in many other pneumococcal strains.