Cell cycle-dependent strand bias for UV-induced mutations in the transcribed strand of excision repair-proficient human fibroblasts but not in repair-deficient cells.
To study the effect of nucleotide excision repair on the spectrum of mutations induced in diploid human fibroblasts by UV light (wavelength, 254 nm), we synchronized repair-proficient cells and irradiated them when the HPRT gene was about to be replicated (early S phase) so that there would be no time for repair in that gene before replication, or in G1 phase 6 h prior to S, and determined the kinds and location of mutations in that gene. As a control, we also compared the spectra of mutations induced in synchronized populations of xeroderma pigmentosum cells (XP12BE cells, which are unable to excise UV-induced DNA damage). Among the 84 mutants sequenced, base substitutions predominated. Of the XP mutants from S or G1 and the repair-proficient mutants from S, approximately 62% were G.C----A.T. In the repair-proficient mutants from G1, 47% were. In mutants from the repair-proficient cells irradiated in S, 71% (10 of 14) of the premutagenic lesions were located in the transcribed strand; with mutants from such cells irradiated in G1, only 20% (3 of 15) were. In contrast, there was no statistically significant difference in the fraction of premutagenic lesions located in the transcribed strand of the XP12BE cells; approximately 75% (24 of 32) of the premutagenic lesions were located in that strand, i.e., 15 of 19 (79%) in the S-phase cells and 9 of 13 (69%) in the G1-phase cells. The switch in strand bias supports preferential nucleotide excision repair of UV-induced damage in the transcribed strand of the HPRT gene.
McGregor
W G
WG
Department of Microbiology, Michigan State University, East Lansing 48824-1316.
Chen
R H
RH
Lukash
L
L
Maher
V M
VM
McCormick
J J
JJ
D001483:Base Sequence; D002460:Cell Line; D004249:DNA Damage; D004260:DNA Repair; D005347:Fibroblasts / Q000166:cytology / Q000528:radiation effects; D016193:G1 Phase; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics* / Q000528:radiation effects; D007399:Interphase; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D016196:S Phase; D014158:Transcription, Genetic; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000378:metabolism
D007041:Hypoxanthine Phosphoribosyltransferase