title: RNase H confers specificity in the dnaA-dependent initiation of replication at the unique origin of the Escherichia coli chromosome in vivo and in vitro.
abstract: Escherichia coli rnh mutants defective in RNase H activity display the features of previously described sdrA (stable DNA replication) and dasF (dnaA suppressor) mutants: (i) sustained DNA replication in the absence of protein synthesis, (ii) lack of requirement for dnaA protein and the origin of replication (oriC), and (iii) sensitivity of growth to a rich medium. Both the sdrA mutants (selected for continued DNA replication in the absence of protein synthesis) and the dasF mutants (selected as dnaA suppressors) are defective in RNase H activity, measured in vitro. Furthermore, a 760-base-pair fragment containing the rnh+ structural gene complements the phenotype of each of the rnh, sdrA, and dasF mutants, indicative of a single gene. One function of RNase H in vivo is in the initiation of a cycle of DNA replication at oriC dependent on dnaA+. In keeping with these results, RNase H contributes to the specificity of dnaA protein-dependent replication initiated at oriC in a partially purified enzyme system.
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D002701:Chloramphenicol / Q000494:pharmacology; D002876:Chromosomes, Bacterial / Q000502:physiology*; D004261:DNA Replication; D004722:Endoribonucleases / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005838:Genotype; D009154:Mutation; D010641:Phenotype; D016914:Ribonuclease H; D013045:Species Specificity; D013489:Suppression, Genetic
chemical_list: D001426:Bacterial Proteins; D002701:Chloramphenicol; D004722:Endoribonucleases; D016914:Ribonuclease H