Nucleotide sequence and genetic organization of the NgoPII restriction-modification system of Neisseria gonorrhoeae.

The NgoPII restriction endonuclease, which recognizes the sequence 5'-GG decreases CC-3', differs from its isoschizomer HaeIII in being sensitive to methylation at the external cytosine residue. The entire nucleotide sequence of a cloned 3.3 kb segment of Neisseria gonorrhoeae strain P9 chromosomal DNA which harbours the NgoPII restriction-modification system has been determined. This data, coupled with sub-cloning experiments, indicates that the restriction endonuclease (R.NgoII) and modification (M.NgoII) genes are transcribed from separate promoters but are arranged in tandem, with the R.NgoPII gene being located on the 5' side of the M.NgoPII gene. Unlike all previously reported restriction systems the 3' end of the endonuclease open reading frame overlaps the 5' end of the methylase open reading frame by 8 codons. This overlap may have implications for the regulation of the NgoPII restriction-modification system.