Escherichia coli strains lacking protein HU are UV sensitive due to a role for HU in homologous recombination.
hupA and hupB encode the alpha and beta subunits of the Escherichia coli histone-like protein HU. Here we show that E. coli hup mutants are sensitive to UV in the rec+ sbc+, recBC sbcA, recBC sbcBC, umuDC, recF, and recD backgrounds. However, hupAB mutations do not enhance the UV sensitivity of resolvase-deficient recG ruvA strains. hupAB uvrA and hupAB recG strains are supersensitive to UV. hup mutations enhance the UV sensitivity of ruvA strains to a much lesser extent but enhance that of rus-1 ruvA strains to the same extent as for rus+ ruv+ strains. Our results suggest that HU plays a role in recombinational DNA repair that is not specifically limited to double-strand break repair or daughter strand gap repair; the lack of HU affects the RecG RusA and RuvABC pathways for Holliday junction processing equally if the two pathways are equally active in recombinational repair; the function of HU is not in the substrate processing step or in the RecFOR-directed synapsis action during recombinational repair. Furthermore, the UV sensitivity of hup mutants cannot be suppressed by overexpression of wild-type or mutant gyrB, which confers novobiocin resistance, or by different concentrations of a gyrase inhibitor that can increase or decrease the supercoiling of chromosomal DNA.
Li
S
S
School of Biological Sciences, University of Wales Swansea, Swansea SA2 8PP, United Kingdom.
Waters
R
R
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D029968:Escherichia coli Proteins; D005819:Genetic Markers; D005838:Genotype; D009154:Mutation; D009675:Novobiocin / Q000494:pharmacology; D011995:Recombination, Genetic; D059005:Topoisomerase II Inhibitors; D014466:Ultraviolet Rays
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005819:Genetic Markers; C031908:H-NS protein, bacteria; C099188:HupA protein, bacteria; D059005:Topoisomerase II Inhibitors; C490937:hupA protein, E coli; D009675:Novobiocin