Figure 1. (A) Genetic organization and expression of the genes of the Type I R-M system of B. bifidum S17. The hsdM, hsdS and hsdR genes (black arrows) encoding the methyltransferase, sequence recognition and restriction subunit are located in close proximity to a putative integrase gene (gray). (B) Genetic organization and expression of the genes encoding the Type II R-M system of B. bifidum S17 with methyltransferase (bbif0710) and restriction endonuclease genes (bbif0711; black arrows) and the adjacent integrase gene (gray). Expression of all genes was analyzed in RNA samples of bacteria harvested in exponential growth phase by reverse transcription PCR. Negative controls (no reverse transcription; middle) and positive controls (PCR on chromosomal DNA, right bands) were included. Gels were loaded with samples as follows: RT-PCRs in lanes 3, 6 and 9 (3: hsdM; 6: hsdS and 9: hsdR in A; 3: bbif0711 and 6: bbif0711 in B) and corresponding negative (lanes 1, 4, 7) and positive controls (lanes 2, 5 and 8).