(A) Methylation of 5′-GATC-3′ sequence in the DNA of various strains of S. suis. Total DNAs from the following strains were treated with two complementary restriction endonucleases and analyzed by agarose gel electrophoresis: Lane 1, NCTC10234; lane 2, DAT1; lane 3, 204; lane 4, 205; lane 5, 207; lane 6, 211; lane 7, 213; lane 8, 220. D, digested with DpnI (specific for methylated sequence); M, digested with MboI (specific for unmethylated sequence). S, 1-kb ladder DNA size standards (GIBCO/BRL). (B) DNA cleavage activities of S. suis crude extracts using the total DNAs of S. suis NCTC10234 (N, unmethylated DNA) and DAT1 (D, methylated DNA) as substrates. Lane numbers for the strains from which the crude extracts were prepared are the same as in panel A. S, 1-kb ladder size standards (GIBCO/BRL). (C) Restriction cleavage activities of the crude extracts using unmethylated pUC19 as the substrate. The lane numbers of the strains from which the crude extracts were prepared match those in panel B. M, pUC19 digested with MboI; S, 100-bp ladder size standards (GIBCO/BRL); Chr, contaminating chromosomal DNA.