Structural homologies among type I restriction-modification systems.

Abstract

Structural homologies among different restriction systems of Escherichia coli and several Salmonella species have been investigated by immunological methods using antibodies prepared against two subunits of the E. coli K12 restriction enzyme, and by DNA hybridization experiments using different fragments of the E. coli K12 hsd genes as probes. The results with both techniques show a strong homology between the E. coli K12 and B restriction‐modification systems, weaker but nevertheless marked homology between E. coli K12 and the Salmonella systems SB, SP, and SQ and, surprisingly, no homology between the E. coli K12 and A systems.

Diversity within the Campylobacter jejuni type I restriction–modification loci

“…Therefore, classification of HsdM families based on amino acid sequence similarity alone has the potential drawback of eventually generating an enormous number of type I R-M families. Analyses based on other criteria, such as allelic complementation and immunological cross-reactivity (Fuller-Pace et al, 1985;Murray et al, 1982;Suri & Bickle, 1985), may be able to place distantly related type I systems (e.g. the type ID and type 'IF' systems) into the same family; however, analyses performed on such diverse taxa may be problematic.…”

Immigration control of DNA in bacteria: self versus non-self

“…Of fundamental influence in our understanding of type I R-M systems has been the demonstration that these enzymes can be considered as members of a family within which the subunits of different enzymes are interchangeable. It came as a surprise, however, that alleles at this locus, in particular those specifying EcoAI in E. coli strain 15T − , encode sufficiently dissimilar type I R-M systems to warrant their separation into a different family (Murray et al, 1982). The initial evidence came from hybridization screens of bacterial DNAs and serological screens of bacterial extracts.…”

The nucleotide sequence recognised by the Escherichia coli D type I restriction and modification enzyme

“…The enzyme was purified by a series of column chromatography steps on DEAE-Sephacel, gel filtration on Sephacryl S-200, heparin agarose and lastly on ATP-agarose. The purification was monitored by the DNA dependent, S-adenosylmethionine (AdoMet) dependent ATPase activity of the enzyme as described in (12) as well as by immunoblotting (13) using antibodies raised against the hsdR and hsdM subunits of EcoK as previously described (7,11). In vitro DNA methylation Methylation of DNA by EcoD was carried out using H-methylAdoMet (Amersham, 64-74 Ci/mmol) as described in (14) with some modifications (11).…”

“…Further, DNA hybridisation experiments using probes derived from the E. coli K12 hsd region have suggested a close similarity between the hsdR and hsdM genes of E. coli K12 and those of several other systems, confirming their allelic nature. Interestingly enough, these experiments showed that there was no such strong homology between the different hsdS genes (7).…”

“…A new type I R-M system, EcoD, from a clinical isolate of E. coli, was described recently and shown to be allelic to the other enzymes from E. coli (7). More recently, the hsdS gene sequence of this system has been determined and compared to that of the EcoK and EcoB hsdS genes (8).…”