Effects of photoreactivation of cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts on ultraviolet mutagenesis in SOS-induced repair-deficient Escherichia coli.
Using purified photolyases for pyrimidine (6-4) pyrimidone photoproducts [(6-4)PP] and cyclobutane pyrimidine dimers (CPD), the effects of photoreactivation on mutagenesis were examined in the supF gene on a plasmid transfected into repair-deficient SOS-induced Escherichia coli host cells. More than 95% of CPD and (6-4)PP were removed from plasmid DNA by treatment with CPD photolyase and (6-4)photolyase, respectively. In each photolyase treatment, base substitutions at dipyrimidine sequences were predominantly observed. Of the single base substitutions observed after CPD photoreactivation, 83% were A:T-->G:C transitions at 5'-TT-3' sites. After (6-4)photolyase treatment, 81% were G:C-->A:T transitions at 5'-CC-3' and 5'-TC-3' sequences. Thus, the major mutagenic photoproducts of single-base substitutions were CPD at 5'-CC-3' or 5'-TC-3' sites and (6-4)PP at 5'-TT-3' sites. Tandem double mutations occurred mainly at 5'-CC-3' sites and were CPD-photoreactivated, suggesting that CPD at 5'-CC-3' was responsible for tandem double mutations. After photoreactivation of both CPD and (6-4)PP, single-base substitutions were primarily G:C-->A:T transitions at 5'-CC-3' or 5'-TC-3' sites and A:T-->G:C transitions at 5'-TT-3' sites, and secondarily G:C-->T:A transversions at 5'-CC-3' sites, G:C-->C:G transversions at 5'-CC-3' sites and A:T-->T:A transversions at 5'-TT-3' sites, which were essentially the same as those observed after photoreactivation of CPD alone, (6-4)PP alone and without photoreactivation. Thus, these transversions were not derived from unknown UV adducts but from incompletely repaired CPD and (6-4)PP.
Tanaka
M
M
Biological Institute, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. tnkm@mail.cc.tohoku.ac.jp
Nakajima
S
S
Ihara
M
M
Matsunaga
T
T
Nikaido
O
O
Yamamoto
K
K
D001483:Base Sequence; D004260:DNA Repair / Q000235:genetics* / Q000528:radiation effects; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000528:radiation effects*; D016153:Genes, Suppressor; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010777:Photochemistry; D010957:Plasmids / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D011740:Pyrimidine Dimers / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D013014:SOS Response, Genetics / Q000235:genetics* / Q000528:radiation effects*; D014466:Ultraviolet Rays
D004269:DNA, Bacterial; D011740:Pyrimidine Dimers; C058406:pyrimidine-pyrimidone dimer; C096275:supF tRNA; D012343:RNA, Transfer; C098727:pyrimidine(6-4)pyrimidone photolyase; D004255:Deoxyribodipyrimidine Photo-Lyase