RRC ID 30134
Author Kogoma T, Hong X, Cadwell GW, Barnard KG, Asai T.
Title Requirement of homologous recombination functions for viability of the Escherichia coli cell that lacks RNase HI and exonuclease V activities.
Journal Biochimie
Abstract rnhA224 and rnhA339::cat mutants which lack RNase HI activity were found to constitutively express the sfiA::lacZ operon fusion in a recA+ lexA(+)-dependent manner. The sfiA::lacZ expression (indicating SOS induction) in rnhA mutants was increased to higher levels by the introduction of the recD1903 or recB21 mutation. The SOS induction in these cells was further enhanced by nutritional shift up from casamino acid medium to Luria broth. Although the extent by which the recD and recB mutations increased the sfiA expression in rnhA mutants was similar, the rnhA224 recB21 double mutant had plating efficiencies that were 25-fold lower on casamino acid plates and 5 x 10(5)-fold lower on Luria broth plates than the respective plating efficiencies of either rnhA224 recD or rnhA::cat recD double mutants. Whereas the recD mutation inactivates the exonuclease activity of the RecBCD (Exo V) enzyme without reducing the recombination proficiency of the mutant, the recB21 mutation abolishes both the exonuclease activity and recombination capability. Therefore, in the absence of both RNase HI and Exo V activities, homologous recombination functions become crucial for viability, particularly in Luria broth. Introduction of mutations in recA, recJ and recN exacerbated the phenotypes. It is proposed that R-loops which persist due to the lack of RNase HI activity can be removed by two alternative routes of DNA repair: one involving Exo V, Exo I and DNA polymerase I, and the other involving both the RecBCD and RecF pathways of homologous recombination activities. The isolation of RNA polymerase mutants that constitutively express the SOS response at high levels and exhibit remarkable broth-sensitivity lend strong support to the contention that increased amounts of the persisting R-loop in rnhA mutants growing in Luria broth give rise to a stronger SOS response.
Volume 75(1-2)
Pages 89-99
Published 1993-1-1
DOI 10.1016/0300-9084(93)90029-r
PII 0300-9084(93)90029-R
PMID 8389213
MeSH DNA Helicases / metabolism* DNA, Bacterial / biosynthesis DNA-Directed RNA Polymerases / genetics Escherichia coli / enzymology* Escherichia coli Proteins* Exodeoxyribonuclease V Exodeoxyribonucleases / metabolism* Mutation* Recombination, Genetic* Ribonuclease H / metabolism* SOS Response, Genetics*
IF 3.362
Times Cited 44
Prokaryotes E. coli ME9103 ME9245 ME9249 ME9406 ME9392 ME9443 ME9444 ME9449 ME9438 ME9439 ME9441 ME9442 ME9427 ME9429 ME9424 ME9425 ME9426 ME9412 ME9413 ME9417 ME9400 ME9402 ME9403 ME9395 ME9399 ME9436 ME9433 ME9435 ME9259 ME9418 ME9440 ME9432 ME9434 ME9330、ME9411 ME9144