Gene organization of the NruI and Sbo13I R-M systems. The nruIM and nruIR genes are transcribed in the opposite direction. There is a gap of 350 bp non-coding sequence between the two genes. The controller gene sbo13IC and sbo13IR gene are transcribed in the same direction. The sbo13IM gene is in the opposite orientation. The NruI and Sbo13I R-M sequences have been submitted to GenBank and assigned the accession number: HM022156 and HM236832, respectively.