Histone-like protein HU is required for recA gene-dependent DNA repair and SOS induction pathways in UV-irradiated Escherichia coli.
OBJECTIVE
Escherichia coli HU protein exists as a heterodimer composed of two highly homologous subunits, HU-1 and HU-2, encoded by the hupB and hupA genes, respectively. It introduces negative supercoils into a relaxed circular DNA. Various roles of HU have been suggested in cellular processes such as DNA replication and transcription. The present experiments were designed to understand the role of HU in DNA repair processes in E. coli.


METHODS
The sensitivity of hupA/hupB mutants of E. coli to the lethal and mutagenic effects of UV was compared with that of a wild-type strain. The effect of the hupAhupB mutations in SOS induction was also examined.


RESULTS
The hupAhupB mutations increased the UV sensitivity of E. coli. Nucleotide excision repair was unaffected by the deficiency of HU. On the other hand, E. coli hupAhupB mutants were sensitive to UV in the recA+recB+recF background but not in the recArecB+recF+ or recA+recBrecF+ background. The frequency of UV-induced mutation to rifampicin resistance was significantly reduced in the hupAhupB mutants, and the induction of the recA::lacZ and umuC::lacZ fusion genes was also suppressed in the mutants.


CONCLUSIONS
HU protein plays a critical role in the recA, recB-dependent recombinational DNA repair and SOS induction pathways in UV-irradiated E. coli.
Miyabe
I
I
Laboratory of Radiation Biology, Graduate School of Science, Kyoto University, Japan.
Zhang
Q M
QM
Kano
Y
Y
Yonei
S
S
D001426:Bacterial Proteins / Q000378:metabolism*; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000528:radiation effects*; D009154:Mutation; D010957:Plasmids; D011836:Radiation Tolerance; D011938:Rec A Recombinases / Q000235:genetics*; D011995:Recombination, Genetic; D013014:SOS Response, Genetics / Q000235:genetics*; D014466:Ultraviolet Rays
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C040330:histone-like protein HU, bacteria; D011938:Rec A Recombinases