title: New restriction enzymes discovered from Escherichia coli clinical strains using a plasmid transformation method.
abstract: The presence of restriction enzymes in bacterial cells has been predicted by either classical phage restriction-modification (R-M) tests, direct in vitro enzyme assays or more recently from bacterial genome sequence analysis. We have applied phage R-M test principles to the transformation of plasmid DNA and established a plasmid R-M test. To validate this test, six plasmids that contain BamHI fragments of phage lambda DNA were constructed and transformed into Escherichia coli strains containing known R-M systems including: type I (EcoBI, EcoAI, Eco124I), type II (HindIII) and type III (EcoP1I). Plasmid DNA with a single recognition site showed a reduction of relative efficiency of transformation (EOT = 10(-1)-10(-2)). When multiple recognition sites were present, greater reductions in EOT values were observed. Once established in the cell, the plasmids were subjected to modification (EOT = 1.0). We applied this test to screen E.coli clinical strains and detected the presence of restriction enzymes in 93% (14/15) of cells. Using additional subclones and the computer program, RM Search, we identified four new restriction enzymes, Eco377I, Eco585I, Eco646I and Eco777I, along with their recognition sequences, GGA(8N)ATGC, GCC(6N)TGCG, CCA(7N)CTTC, and GGA(6N)TATC, respectively. Eco1158I, an isoschizomer of EcoBI, was also found in this study.
authors.affiliation: Division of Microbiology and Molecular Genetics, Department of Biochemistry and Microbiology, School of Medicine, Loma Linda University, Loma Linda, CA 92350, USA.
authors.forename: Julie K A
authors.initials: JK
authors.lastname: Kasarjian
authors.forename: Masatake
authors.initials: M
authors.lastname: Iida
authors.forename: Junichi
authors.initials: J
authors.lastname: Ryu
mesh_terms: D001665:Binding Sites / Q000235:genetics; D004262:DNA Restriction Enzymes / Q000378:metabolism*; D015280:DNA Restriction-Modification Enzymes / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D014170:Transformation, Genetic
chemical_list: D015280:DNA Restriction-Modification Enzymes; D004262:DNA Restriction Enzymes