Transformation in Streptococcus pneumoniae: mosaic genes and the regulation of competence.

The presence of highly divergent mosaic blocks in penicillin binding protein genes responsible for penicillin resistance in Streptococcus pneumoniae implies that transformation is an important tool for the evolution of this pathogen. Genetic competence depends on production of the competence signaling peptide CSP, the processed product of comC, which is curiously part of a mosaic gene arrangement itself. Expression of comC is part of a complex regulatory network involving at least two receptor kinase/transcriptional regulator pairs: ComD/E, which is responsible for induction, and CiaH/R, which inhibits expression of the comCDE operon.