Overexpression of RNase H partially complements the growth defect of an Escherichia coli delta topA mutant: R-loop formation is a major problem in the absence of DNA topoisomerase I.

TLDR: It is shown 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, and a defect in DNA gyrase can correct several phenotypes associated with a mutation in the rnhA gene, which encodes the majorRNase H activity.

Abstract: 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