Fig. 1
Typical gene arrangement and promoter orientation in convergent and divergent R-M systems. a Convergent systems, a representative of which is AhdI, where other studied systems encoding C protein include Esp1396I, Kpn2I, Csp231I, PvuII [14, 23, 47–49]. Note that C and R genes are transcribed together from PCR promoter. Transcription of M is exhibited from the separate PM promoter. b Divergent systems, a representative of which is EcoRV, where BamHI is another studied divergent system that encods C protein [20]. C and R genes are also co-transcribed, but now share a common promoter region with M gene. In EcoRV the two divergent promoters (PCR and PM) have overlapping RNA polymerase binding sites