Alkylations at base nitrogens in DNA are removed by excision repair, the first step of which is catalyzed by the repair enzyme N-methylpurine-DNA glycosylase (MPG). To study regulation of MPG expression, we have cloned the rat MPG promoter. A cosmid clone containing the rat MPG gene was isolated from a library using rat MPG cDNA as a probe. The 5' part of the MPG gene and the nontranscribed 5'-flanking region were isolated and characterized. Transcription start sites of the rat MPG gene were identified by primer extension and S1 nuclease protection analysis of RNA from primary rat hepatocytes. Promoter activity of the 5'-flanking noncoding region was shown by transfection in H4IIE rat hepatoma cells of various genomic MPG fragments cloned in front of the reporter gene chloramphenicol acetyltransferase. The rat MPG promoter does not contain a TATA box, but has a CCAAT sequence element and putative binding sites for the transcription factors Sp1, AP-2, AP-3, Ets-1, PEA3, NF-1, p53, c-Myc, NF-kappa B, and the glucocorticoid receptor. The activity of the rat MPG promoter was found to be inducible by the tumor promoter TPA and UV light, but not to a significant extent by methylating agents and ionizing radiation.