title: RNase H-defective mutants of Escherichia coli: a possible discriminatory role of RNase H in initiation of DNA replication.
abstract: Mutants of Escherichia coli completely deficient in RNase H activity were isolated by inserting transposon Tn3 into the structural gene for RNase H, rnh, and its promoter. These rnh- mutants exhibited the following phenotypes; (1) the mutants grew fairly normally, (2) rnh- cells could be transformed with ColE1 derivative plasmids, pBR322 and pML21, though the plasmids were relatively unstable, under non selective conditions, (3) rnh- mutations partially suppressed the temperature-sensitive phenotype of plasmid pSC301, a DNA replication initiation mutant derived from pSC101, (4) rnh- mutations suppressed the temperature-sensitive growth character of dnaAts mutant, (5) rnh- cells showed continued DNA synthesis in the presence of chloramphenicol (stable DNA replication). Based on these findings we propose a model for a role of RNase H in the initiation of chromosomal DNA replication. We suggest that two types of RNA primers for initiation of DNA replication are synthesized in a dnaA/oriC-dependent and -independent manner and that only the dnaA/oriC-dependent primer is involved in the normal DNA replication since the dnaA/oriC independent primer is selectively degraded by RNase H.
mesh_terms: D004261:DNA Replication; D004251:DNA Transposable Elements; D004722:Endoribonucleases / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005838:Genotype; D009154:Mutation; D010641:Phenotype; D010957:Plasmids; D016914:Ribonuclease H; D013045:Species Specificity
chemical_list: D004251:DNA Transposable Elements; D004722:Endoribonucleases; D016914:Ribonuclease H