ComCED signal loop precisely regulates nlmC expression in Streptococcus mutans

Abstract

The ComED two-component signal transduction system (TCSTS) and the exogenous CSP can provoke the competence development and mutacin production of Streptococcus mutans. More binding fashions of ComE with DNA are the molecular basis for the ComED TCSTS to play pleiotropic roles. The interaction of nlmC and comC in regulation makes the expression of nlmC different from that of nlmAB and the ComE molecular feature is shown in the regulation pattern of nlmC. By electrophoretic mobility shift assay, ComE binding sites were discoveried in PnlmC314 and PnlmC419 for the first time. In the wild-type background, the promoter activity of nlmC is not only stronger than that of nlmAB but also rushes to a peak value of 3,116.0 MU at the point of 100 min in liquid culture with no supply of exogenous CSP; the data indicate that the regulation of nlmC expression is charged in an known coordination mechanism. In the mutant background, by monitoring the promoter activity of nlmC and nlmAB, it is proved that they are both controlled directly by the ComED TCSTS. But the surprising result is the deletion of comC to make nlmC promoter lose its activity completely. Based on those data, it is deduced that Pnlm419, PnlmC314 and PnlmC, which comprise the nlmC regulating region, coordinate to incite nlmC expression and to make nlmC expression different from that of nlmAB because of a synergistic effect, whereas they also could inhibit comC expression by blocking the RNA polymerase moving through the binding of ComE with the comC encoding region.