Overexpression of RNase H Partially Complements the Growth Defect of an Escherichia coli ΔtopA Mutant: R-Loop Formation is a Major Problem in the Absence of DNA Topoisomerase I

• Published in: Proceedings of the National Academy of Sciences - PNAS 1995-04, Vol.92 (8), p.3526-3530
• Main Authors: Drolet, Marc, Phoenix, Pauline, Menzel, Rolf, Massé, Eric, Liu, Leroy F., Crouch, Robert J.
• Format: Article
• Language: English
• Subjects: Alleles; Amino acids; Bacteriophages; Cold Temperature; DNA; DNA Topoisomerases, Type I - deficiency; DNA, Bacterial - metabolism; Escherichia coli; Escherichia coli - genetics; Escherichia coli - growth & development; Genes; Genetic Complementation Test; Genetic inheritance; Genetic mutation; Nucleic Acid Conformation; Nucleic Acid Heteroduplexes - metabolism; Phenotype; Phenotypes; Plasmids; Ribonuclease H - biosynthesis; Ribonuclease H - genetics; RNA; RNA, Bacterial - metabolism; Transcription, Genetic
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.8.3526

Previous biochemical studies have suggested a role for bacterial DNA topoisomerase (TOPO) I in the suppression of R-loop formation during transcription. In this report, we present several pieces of genetic evidence to support a model in which R-loop formation is dynamically regulated during transcription by activities of multiple DNA TOPOs and RNase H. In addition, our results suggest that events leading to the serious growth problems in the absence of DNA TOPO I are linked to R-loop formation. We show that the overexpression of RNase H, an enzyme that degrades the RNA moiety of an R loop, can partially compensate for the absence of DNA TOPO I. We also note that a defect in DNA gyrase can correct several phenotypes associated with a mutation in the rnhA gene, which encodes the major RNase H activity. In addition, we found that a combination of topA and rnhA mutations is lethal.