title: Conservation of organization in the specificity polypeptides of two families of type I restriction enzymes.
abstract: We have identified the recognition sequence for the Citrobacter freundii restriction endonuclease CfrA, a member of the A-family of type I R-M enzymes. This bipartite target sequence differs in both its components from those of other type I enzymes. We determined the nucleotide sequence of its specificity gene (hsdS) and a comparison of this with its relative EcoA identifies two extensive variable regions, an organization analogous to that found in the K-family of type I R-M enzymes. The specificity polypeptides of the A-family, unlike those of K, have an N-terminal conserved region, and this includes a sequence repeated within the central conserved region. A second repeat sequence, identified at the amino acid level, coincides with the only sequence similarity common to all type I S polypeptides. Sequences immediately downstream from the hsdS genes of EcoA, CfrA, EcoK, B and D are almost identical, consistent with an allelic chromosomal location.
authors.affiliation: Department of Molecular Biology, University of Edinburgh, U.K.
authors.forename: P
authors.initials: P
authors.lastname: Kannan
authors.forename: G M
authors.initials: GM
authors.lastname: Cowan
authors.forename: A S
authors.initials: AS
authors.lastname: Daniel
authors.forename: A A
authors.initials: AA
authors.lastname: Gann
authors.forename: N E
authors.initials: NE
authors.lastname: Murray
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002954:Citrobacter / Q000201:enzymology*; D003062:Codon; D004269:DNA, Bacterial; D015253:Deoxyribonucleases, Type I Site-Specific / Q000235:genetics*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D003062:Codon; D004269:DNA, Bacterial; D010455:Peptides; C061993:endodeoxyribonuclease CfrA; D015253:Deoxyribonucleases, Type I Site-Specific