RESTRICTION AND MODIFICATION SYSTEMS OF NEISSERIA-GONORRHOEAE

An individual strain of Neisseria gonorrhoeae may produce up to 16 dif ferent DNA methytransferases (MTases). We have used a novel cloning sy stem that is able to detect MTase clones in the absence of direct sele ction [Piekarowicz et al., Nucleic Acids Res. 19 (1998)1831-1835] to i dentify 14 different MTase clones. Initial characterization of these c lones indicates that at least seven of these MTases are linked to rest riction endonuclease (ENase) systems. Six of these systems have been c haracterized by DNA sequence analysis, and the open reading frames enc oding each of these systems have been identified. The recognition sequ ences for the cloned systems have the following specificities: S.NgoI, RGCGCY; S.NgoII, GGCC; S.NgoIV, GCCGCC; S.NgoV, GGNNCC; S.NgoVII, GCS GC; S.NgoVIIIA, GGTGA; and S.NgoVIIIC, TCACC. Of those systems that ha ve been cloned, NgoI-NgoVII are typical type II R-M systems, with each encoding a DNA MTase that methylates cytosine in position 5. NgoVIII is a type IIS system, containing an ENase and two different MTases. On e of these is a cytosine MTase (NgoVIIIC) and the other is an adenine MTase (NgoVIIIA). Although most of our clones encodes both the ENase a nd the MTase, none of the six R-M systems are genetically linked on th e chromosome.