ORGANIZATION AND EXPRESSION OF THE MOUSE GENE FOR DNA-REPAIR METHYLTRANSFERASE

O-6-Methylguanine-DNA methyltransferase (MGMT) is present in various o rganisms, from bacteria to human cells, and plays an important role in preventing mutations caused by alkylating substances, To understand b etter the regulatory mechanism involved in the expression of the gene and to construct a mouse model to investigate roles of the enzyme in c arcinogenesis, the genomic sequence for mouse methyltransferase was is olated and characterized, The gene consists of 5 exons and spans over 180 kb, whereas mRNA for the enzyme was less than 1 kb. The promoter r egion for the gene is CC-rich, contains many Sp1 recognition sequences and lacks typical TATA and CCAAT boxes, Primer extension and S1 mappi ng revealed the existence of multiple transcription initiation sites, among which a major site was defined as +1. The putative promoter regi on was placed upstream of the chloramphenicol acetyltransferase (CAT) reporter gene and the construct was introduced into mouse NIH-3T3 cell s, Deletion analyses revealed that a sequence from -262 to +56 carries the basic promoter activity. In addition, an adjacent region, spannin g from +56 to +95, carries an E2F-like element that greatly stimulates the frequency of transcription, Alteration of TTTTGGGGC to TTAACGGGC considerably reduced the activity.