Human cDNA expressing a functional DNA glycosylase excising 3-methyladenine and 7-methylguanine.

A cDNA expression library from a human cell line was introduced into an E. coli strain deficient in the repair of 3-meAde bases in DNA. E. coli strains deficient in the repair of 3-meAde are unusually sensitive to DNA methylating agents. A plasmid pANPG10 (Alkyl-N-Purine-DNA Glycosylase) was rescued from the library based on its ability to reduce the sensitivity of the mutant strain to methylmethane sulfonate. Crude extracts of the E. coli mutant strain hosting the plasmid pANPG10 release both 3-meAde and 7-meGua from DNA. The longest open reading frame in the sequence codes for a polypeptide of 230 amino acids of molecular weight 25.5 kD, with a pI of 9.1. The derived amino acid sequence of the human 3-meAde-DNA glycosylase has 85% sequence identity with the 3-meAde-DNA glycosylase from rat hepatoma cells.