SELECTIVITY OF THE EXCISION OF ALKYLATION PRODUCTS IN A XERODERMA PIGMENTOSUM-DERIVED LYMPHOBLASTOID LINE

Lymphoblastoid cells derived from a complementation group C xeroderma patient were unable to remove 06-methyl guanine residues formed in DNA by treatment of cells with low concentrations of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). The xeroderma cells were competent in their ability to excise 3-methyl adenine adducts. MNNG treatment induced excision repair in the xeroderma line and in addition the treatment resulted in the presence of numerous single-strand breaks in the DNA. The single gene, UV-excision-defective mutants of Escherichia coli, uvrA and uvrB, are able to excise MNNG- induced 06-methyl guanine adducts indicating that excision of this compound is not due to operation of the UV endonuclease system. © 1979.