Table 2.

The list of orthologous R-M systems groups, which include putative separated R-M systems

Number of group	Type	Taxon	Number of R-M systems	Number of R-M systems annotated in REBASE	Number of separated R-M systems	Number of solitary REs
1	II	Bordetella: three species	3	2	1	1
2	II	Proteobacteria: three classes	5	2	3	3
3	II	α-Proteobacteria: four orders	5	0	5	5
4	II	Clostridium perfringens: three strains	3	0	3	3
5	II	Fibrobacter succinogenes: two strains	2	0	2	2
6	II	Bacteroides: two species	2	0	2	2
7	II	Bacteroides: three species	3	0	3	3
8	I	Archaea, Bacteria	79	29	50 a	27 b
9	I	Archaea, Bacteria	101	100	4	4
10	I	Archaea, Bacteria	24	23	1	1
11	I	Archaea, Bacteria	128	122	6	6

^aThe functionality of separated R-M systems from three strains of S. aureus has been proved experimentally [9]; see also text.

^bOf the 27 solitary REs, 25 are from strains of S. aureus, 23 S. aureus strains contain 1 RE gene and 2 cassettes of genes of MTase and S-proteins. This is why the number of separated R-M systems exceeds the number of solitary REs.