Removal of O6-methylguanine from DNA of normal and xeroderma pigmentosum-derived lymphoblastoid lines

Abstract

Certain [human] xeroderma pigmentosum cell lines, deficient in dimer excision, are also unable to remove O6-MeG [O6-methylguanine]. Removal of O6-MeG occurs rapidly with a half-life of < 1 h. Two cell types can be distinguished: mex+, which remove O6-MeG residues produced by incubation with 0.5 .mu.g/ml MNNG [N-methyl-N''-nitro-N-nitrosoquanidine] and mex- cells, which are unable to remove the adduct. Xeroderma pigmentosum-derived lymphoblastoid lines of complementation groups A, C or D may be either mex+ or mex-. The biochemical mechanism for the removal of O6-MeG in human cells is distinct from the excision of adducts produced by compounds, such as N-acetoxy-N-2-acetylaminofluorene (AAAF), or by UV irradiation; it is not, however, clear whether the distinction between mex+ and mex- lines is genetic or epigenetic.