The restriction-modification system of Pasteurella haemolytica is a member of a new family of type I enzymes.
Genes encoding the type I restriction-modification (R-M) system of the bovine pathogen, Pasteurella haemolytica, have been identified immediately downstream of a locus that encodes a transcriptional activator of P. haemolytica leukotoxin expression. Type I enzymes are encoded by three genes called hsdM, hsdS and hsdR, and have fallen into three groups, called Ia, Ib and Ic. HsdS provides a sequence recognition function which in concert with HsdM forms an active methyltransferase (MTase). Inclusion of the HsdR subunit in the complex creates an active restriction endonuclease (ENase) capable of cleaving unmethylated target DNA. The P. haemolytica hsdMSR genes were mapped using transposon Tn10d-Cam insertions, and bacteriophage restriction and modification assays in Escherichia coli. We determined the nucleotide sequences of hsdM, hsdS and hsdR, and observed that the deduced amino acid (aa) sequences were very similar to predicted R-M subunits in the respiratory pathogen, Haemophilus influenzae. Phylogenetic comparisons of all known Hsd aa sequences placed the P. haemolytica and H. influenzae proteins into a new group which we labeled the Type Id R-M family. Expression of the P. haemolytica R-M genes in E. coli was inefficient and is likely to be a consequence of the unusual codon usage in P. haemolytica genes.
Highlander
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Department of Microbiology and Immunology, Baylor College of Medicine, Houston, TX 77030, USA. sarahh@bcm.tmc.edu
Garza
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D000595:Amino Acid Sequence; D015254:DNA Modification Methylases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements; D015253:Deoxyribonucleases, Type I Site-Specific / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005798:Genes, Bacterial; D016978:Mannheimia haemolytica / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D010957:Plasmids; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000145:classification / Q000235:genetics / Q000378:metabolism
D004251:DNA Transposable Elements; D015254:DNA Modification Methylases; C072994:EcoR124 modification methylase type I; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D015253:Deoxyribonucleases, Type I Site-Specific