Structural analysis of CrfP homologous proteins in Streptococcus. A Promoter motif (CIN box) of natural transformation-related core genes regulated by ComX. B Conserved motif in the crfP gene promoter. C A qRT-PCR analysis showed that crfP was influenced by ComR and ComX under competence. The transcription level did not increase in the absence of the comR or comX gene. D Domain organization of murein hydrolases from different species of streptococci: CHAP, cysteine, histidine-dependent amidohydrolases; SH3, binds peptidoglycan; choline-binding, binds choline residues linked to teichoic acid; conserved domain, uncharacterized domain. The gene from each streptococcal species has the locus tags listed in Additional file 2.