A positive feedback loop mediated by SigmaX enhances expression of the streptococcal regulator ComR. Streptococcus mutans UA159

The transient nature of competence in Bacillus subtilis and in streptococci of the ComCDE class of competence systems, such as S. pneumoniae, is supported by positive feedback loops that induce the expression of their pheromones and the cognate regulators. Most of the streptococci, however, belong to the ComRS regulatory class, in which induction of the pheromones are aslo observed, but with no regulatory mechanisms that would possible regulated the expression of ComR.