title: Influence of phage T3 and T7 gene functions on a type III(EcoP1) DNA restriction-modification system in vivo.
abstract: The ocr+ gene function (gp 0.3) of bacteriophages T3 and T7 not only counteracts type I (EcoB, EcoK) but also type III restriction endonucleases (EcoP1). Despite the presence of recognition sites, phage DNA as well as simultaneously introduced plasmid DNA are protected by ocr+ expression against both the endonucleolytic and the methylating activities of the EcoP1 enzyme. Nevertheless, the EcoP1 protein causes the exclusion of T3 and T7 in P1-lysogenic cells, apparently by exerting a repressor-like effect on phage gene expression. T3 which induces an S-adenosylmethionine hydrolase is less susceptible to the repressor effect of the SAM-stimulated EcoP1 enzyme. The abundance of EcoP1 recognition sites in the T7 genome is explained by their near identity with the T7 DNA primase recognition site.
mesh_terms: D004261:DNA Replication; D004262:DNA Restriction Enzymes; D004269:DNA, Bacterial / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D005814:Genes, Viral; D007700:Kinetics; D009154:Mutation; D013604:T-Phages / Q000235:genetics*; D014169:Transformation, Bacterial; D014779:Virus Replication
chemical_list: D004269:DNA, Bacterial; D004279:DNA, Viral; D004262:DNA Restriction Enzymes