Expression of the endogenous O6-methylguanine-DNA-methyltransferase protects Chinese hamster ovary cells from spontaneous G:C to A:T transitions.
We have investigated whether the presence of a DNA repair enzyme, O6-methylguanine-DNA-methyltransferase (MGMT), affects the nature of spontaneous mutations in a mammalian cell line. We compared spontaneous mutations in the adenine phosphoribosyl transferase gene of a Chinese hamster ovary (CHO) cell line that expressed 14,000 MGMT molecules/cell with those in the parental CHO cells lacking this DNA repair activity. The mutation rate/cell/generation of the two CHO cell lines did not differ significantly. However, DNA sequence analysis of spontaneous mutations in the MGMT-proficient CHO cell line revealed a complex picture. No significant difference from the parental CHO cells was found in the number or type of deletions, frameshifts, multiple substitutions, or insertions. The frequency of G:C to T:A transversions was elevated in MGMT-proficient CHO cells. Expression of the enzyme considerably reduced G:C to A:T transitions (25% versus 8.3%). This latter result is the first evidence that this protein is active on an endogenous source of O6-methylguanine that is normally responsible for spontaneous G:C to A:T transition mutations.
Aquilina
G
G
Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanità, Rome, Italy.
Biondo
R
R
Dogliotti
E
E
Meuth
M
M
Bignami
M
M
D000228:Adenine Phosphoribosyltransferase / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D016466:CHO Cells / Q000201:enzymology*; D006224:Cricetinae; D005091:Exons / Q000235:genetics; D016368:Frameshift Mutation; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D008780:Methyltransferases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase
D006147:Guanine; C008449:O-(6)-methylguanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000228:Adenine Phosphoribosyltransferase