An unexpectedly high excision capacity for mispaired 5-hydroxymethyluracil in human cell extracts.
The oxidation of thymine in DNA can generate a base pair between 5-hydroxymethyluracil (HmU) and adenine, whereas the oxidation and deamination of 5-methylcytosine (5mC) in DNA can generate a base pair between HmU and guanine. Using synthetic oligonucleotides containing HmU at a defined site, HmU-DNA glycosylase activities in HeLa cell and human fibroblast cell extracts have been observed. An HmU-DNA glycosylase activity that removes HmU mispaired with guanine has been measured. Surprisingly, the HmU:G excision activity is 60 times greater than the corresponding HmU:A activity, even though the expected rate of formation of the HmU:A base pair exceeds that of the HmU:G base pair by a factor of 10(7). The HmU:G mispair would arise from the 5mC:G base pair, and, if unrepaired, would give rise to a transition mutation. The observation of an unexpectedly high HmU:G glycosylase activity suggests that human cells may encounter the HmU:G mispair much more frequently than expected. The conversion of 5mC to HmU must be considered as a potential pathway for the generation of 5mC to T transition mutations, which are often found in human tumors.
Rusmintratip
V
V
Divisions of Pediatrics and Molecular Medicine, City of Hope National Medical Center, 1500 East Duarte Road, Duarte, CA 91010, USA.
Sowers
L C
LC
D000225:Adenine / Q000378:metabolism; D020029:Base Pairing; D002457:Cell Extracts; D002460:Cell Line; D004249:DNA Damage; D045647:DNA Glycosylases; D004260:DNA Repair; D005347:Fibroblasts / Q000166:cytology; D006147:Guanine / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009699:N-Glycosyl Hydrolases / Q000378:metabolism*; D010432:Pentoxyl / Q000031:analogs & derivatives / Q000378:metabolism*
D002457:Cell Extracts; C008055:5-hydroxymethyluracil; D006147:Guanine; D010432:Pentoxyl; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D000225:Adenine