The Neisseria gonorrhoeae S.NgoVIII restriction/modification system: a type IIs system homologous to the Haemophilus parahaemolyticus HphI restriction/modification system

Abstract

Strains of Neisseria gonorrhoeae possess numerous restriction-modification (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 system. We cloned two adjacent methyltransferase genes (dcmH and damH), each encoding proteins whose actions protect DNA from digestion by R.HphI or R.Ngo BI (5'TCACC 3'). The damH gene product is a N 6-methyladenine 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 N 6-methyladenine in the DNA. A second plasmid, containing overlapping damH and Escherichia coli dam recognition sequences in combination with various restriction digests, was used to identify which adenine in the recognition sequence was modified by damH. The predicted dcmH gene product is homologous to 5-methylcytosine methyltransferases. The products of both the dcmH and damH genes, as well as an open reading frame downstream of the damH gene are highly similar to the Haemophilus parahaemolyticus hphIMC , hphIMA and hphIR gene products, encoding the Hph I Type IIs 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 system.

Regulation of the HpyII restriction–modification system of Helicobacter pylori by gene deletion and horizontal reconstitution

“…Study of the closely related isolates from a Dutch family provides evidence that a population of H. pylori cells could regulate its R–M function by deletion from the chromosome and reacquisition by natural transformation and homologous recombination. The parallel organization of the hpy 188I R–M locus (Xu et al ., 2000b) suggests that this may be a general mechanism for H. pylori , and possibly for other naturally competent organisms that have direct repeats flanking R–M systems, such as Haemophilus parahaemolyticus (Lubys et al ., 1996; Gunn and Stein, 1997).…”

Restriction-Modification Systems as Minimal Forms of Life

“…Some restriction-modification gene homologues are found to be flanked by long (in the order of 100 bp) direct repeats (Lubys et al 1996;Gunn and Stein 1997;Nobusato et al 2000b;Aras et al 2001). The comparison of two genomes of H. pylori has suggested that this duplication is generated when a restriction-modification gene complex inserts itself into the genome (Fig.…”

Differential Distribution of Novel Restriction-Modification Systems in Clonal Lineages of Neisseria meningitidis

“…Horizontal gene transfer of R-M systems between bacterial species has been described, and it has been suggested that this transfer contributes to the wide distribution of bacterial R-M systems (28). Examples for this phenomenon are sequence similarities between gonococcal and Haemophilus R-M systems (22,47).…”