Specificities of Eleven Different DNA Methyltransferases of Helicobacter pylori Strain 26695

Abstract

Methyltransferases (MTases) of procaryotes affect general cellular processes such as mismatch repair, regulation of transcription, replication, and transposition, and in some cases may be essential for viability. As components of restriction-modification systems, they contribute to bacterial genetic diversity. The genome of Helicobacter pylori strain 26695 contains 25 open reading frames encoding putative DNA MTases. To assess which MTase genes are active, strain 26695 genomic DNA was tested for cleavage by 147 restriction endonucleases; 24 were found that did not cleave this DNA. The specificities of 11 expressed MTases and the genes encoding them were identified from this restriction data, combined with the known sensitivities of restriction endonucleases to specific DNA modification, homology searches, gene cloning and genomic mapping of the methylated bases m 4 C, m 5 C, and m 6 A.The bacterium Helicobacter pylori chronically infects the upper gastrointestinal tract of the majority of people worldwide and is major cause of chronic gastritis and peptic ulcer disease and an early risk factor for gastric cancer (39). H. pylori strains are diverse genetically (1,2,4,16,21,44), and certain strain differences may contribute to the diversity of clinical outcome of infection (13,15,47). Analyses of genome sequences of H. pylori strains 26695 (46) and J99 (3) revealed that each strain contained more than two dozen genes likely to encode DNA methyltransferases (MTases), far more than have been detected in other bacterial genomes to date (20). These MTase genes comprise a large fraction of all genes that were specific to one or the other strain. Bacterial MTases exist either as components of restriction-modification (R-M) systems or as separate enzymes. The former are strain specific, and their main function is to protect host DNA from damage by a cognate restriction enzyme (RE). Separate MTases, which tend to be present in all strains of a species (species-specific MTases), are involved in general cellular processes such as regulation of transcription of specific genes (5, 48), DNA replication (32), mismatch repair (33), or DNA transposition (40). Certain of them can be essential for viability (43) or contribute to specificity in bacterium-host interactions or virulence in pathogens (8,17).Most MTase genes found in the genomes of H. pylori strains 26695 and J99 probably belong to R-M systems. That certain R-M systems might also affect bacterium-host interactions was suggested by induction of transcription of iceA1, a homolog of RE NlaIII, by H. pylori-host cell contact (36). Although iceA1 does not encode a functional protein in most H. pylori strains (14), it is adjacent to a generally active MTase gene (hpyIM) specific for sites recognized by NlaIII. Thus, the hpyI-iceA1 pair may represent a vestige of an R-M system that has evolved some special function relevant to host-pathogen interactions (14). By extrapolation, the same might be true for the MTases of other putative R-M systems in H. pylori. The identification ...

Inflammatory Processes Triggered by Helicobacter pylori Infection Cause Aberrant DNA Methylation in Gastric Epithelial Cells

“…These results indicated that HP itself was not necessary for methylation induction once inflammation was induced by it. This finding is important because a direct role of HP is suggested by the facts that the SHP2 oncoprotein is deregulated by injection of virulent factors such as CagA into GECs (34) and HP possesses multiple DNA (cytosine-5) methyltransferases (35).…”

Molecular Pathways: Involvement of Helicobacter pylori–Triggered Inflammation in the Formation of an Epigenetic Field Defect, and Its Usefulness as Cancer Risk and Exposure Markers

“…First, because H. pylori possesses multiple DNA methyltransferases (46) and a type IV secretion system [a syringe-like structure capable of delivering bacterial materials into a host cell (47) H. pylori infection Figure 1. Formation of epigenetic field for cancerization by chronic inflammation triggered by H. pylori infection.…”

Evolutionary History of hrgA , Which Replaces the Restriction Gene hpy IIIR in the hpy III Locus of Helicobacter pylori

“…Helicobacter pylori, a gram-negative bacterium that colonizes the human stomach, affects the risk of getting upper gastrointestinal tract diseases, including gastric cancer (13). H. pylori strains are highly heterogeneous in terms of the number and nature of the R-M systems that they carry (2,10,11,18,19,21,23). During characterization of the hpyIIIR-hpyIIIM locus in Asian and Western strains, we found numerous strains with a novel gene that we designated hrgA in place of hpyIIIR (encoding an isoschizomer of Moraxella bovis MboI).…”