THE NEISSERIA-GONORRHOEAE S.NGOVIII RESTRICTION MODIFICATION SYSTEM -A TYPE IIS SYSTEM HOMOLOGOUS TO THE HAEMOPHILUS PARAHAEMOLYTICUS HPHIRESTRICTION/MODIFICATION SYSTEM/

Strains of Neisseria gonorrhoeae possess numerous restriction-modifica tion (R-M) systems, One of these systems, which has been found in all strains tested, encodes the S.NgoVIII specificity (5' TCACC 3') R-M sy stem, We cloned two adjacent methyltransferase genes (dcmH and damH), each encoding proteins whose actions protect DNA from digestion by R.H phI or R.NgoBI (5' TCACC 3'), The damH gene product is a N6-methyladen ine methyltransferase that-recognizes this sequence, We constructed a plasmid containing multiple copies of the S.NgoVIII sequence, grew it in the presence of damH and used the HPLC to demonstrate the presence of N6-methyladenine in the DNA, A second plasmid, containing overlappi ng damH and Escherichia coli dam recognition sequences in combination with various restriction digests, was used to identify which adenine i n the recognition sequence was modified by damH, The predicted dcmH ge ne product is homologous to fi-methylcytosine methyltransferases, The products of both the dcmH and damH genes, as well as an open reading f rame downstream of the damH gene are highly similar to the Haemophilus parahaemolyticus hphIMC, hphIMA and hphIR gene products, encoding the HphI Type Ils R-M system, The S.NgoVIII R-M genes are flanked by a 97 bp direct repeat that may be involved in the mobility of this R-M sys tem.