MPG(N-methylpurine-DNA glycosylase) also known as MDG, 3-METHYLADENINE DNA GLYCOSYLASE, 3MeAde DNA GLYCOSYLASE, AAG or APNG. The MPG gene is mapped to human chromosome 16 by analysis of a panel of DNAs from mouse/human and hamster/human hybrid cell lines. The MPG gene was expressed in all cell lines and tissues examined, but was found at particularly high levels in a colon adenocarcinoma cell line (HT29). The completely characterized human MPG gene was found to span 7 to 8 kb of genomic DNA and to be localized 75 kb upstream of the embryonic zeta-globin gene. To assess the contribution of Apng to the repair of several mutagenic lesions in vivo, Hang et al. (1997) biochemically analyzed cell-free extracts of tissues from mice with a targeted deletion of the Apng gene. Following treatment with DNA-methylating agents, increased persistence of 7-methylguanine (meG) was found in liver sections of APNG knockout mice in comparison with wildtype mice, demonstrating an in vivo phenotype for the APNG-null animals.