title: Conservation of complex DNA recognition domains between families of restriction enzymes.
abstract: One polypeptide, designated S, confers sequence-specificity to the multisubunit type I restriction enzymes. Two families of such enzymes, K and A, include members that recognize diverse, bipartite, target sequences. The S polypeptides of the K family, while having areas of near identity, also contain two extensive regions of variable sequence. We now show that one of these, comprising the N-terminal 150 amino acids, specifies recognition of one component of the bipartite target sequence. We have determined the sequence recognized by EcoE, a member of the A family. This sequence, 5'GAG(N7)ATGC, has the trinucleotide GAG in common with EcoA and with StySB of the K family. We determined the nucleotide sequences of the S genes of EcoA and EcoE, and compared their predicted amino acid sequences with each other and with those of the five members of the K family. There is no general sequence similarity between families, but the domain of the S polypeptide of StySB, which specifies GAG, shows nearly 50 per cent identity with the amino variable region of the S polypeptides of EcoA and EcoE. A complex domain that recognizes and directs methylation of GAG is therefore common to enzymes of generally dissimilar amino acid sequence.
authors.affiliation: Department of Molecular Biology, University of Edinburgh, Scotland.
authors.forename: G M
authors.initials: GM
authors.lastname: Cowan
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; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000502:physiology*; D015253:Deoxyribonucleases, Type I Site-Specific / Q000502:physiology*; D004926:Escherichia coli / Q000201:enzymology*; D008745:Methylation; D008969:Molecular Sequence Data; D013379:Substrate Specificity
chemical_list: D004268:DNA-Binding Proteins; D015253:Deoxyribonucleases, Type I Site-Specific