The mouse DNA methyltransferase 5'-region. A unique housekeeping gene promoter.

We have cloned and characterized 5'-flanking sequences of the DNA methyltransferase (MeTase) gene. DNA MeTase gene transcription is initiated at a few discrete sites: 343 and 90 base pairs upstream of the translation initiation site as determined by RNase protection and primer extension assays. The promoter sequences that regulate expression of DNA MeTase, as defined by chloramphenicol acetyltransferase assays, reside between position -171 and the transcription start site. The promoter of DNA MeTase does not contain TATAA or CAAT boxes and is unusual because it does not contain the CG-rich elements characteristic of TATAA-less housekeeping genes. The 5'-flanking region of DNA MeTase contains AP-1, AP-2 and glucocorticoid response elements, suggesting possible regulation by cellular signal transduction pathways. The base composition of the DNA MeTase promoter is markedly different from that of other housekeeping genes. Whereas most housekeeping genes are characterized by CG-rich areas in their 5'-flanking regions, the TG dinucleotide is over-represented in DNA MeTase 5'-flanking sequences, including a perfect tandem repeat of T/G between positions -685 and -650. DNA methylation patterns play an important role in the developmental regulation of gene expression in vertebrates. DNA MeTase activity is probably regulated to maintain this pattern of methylation. We suggest that the DNA MeTase promoter represents a new class of housekeeping gene promoters that was designed to ensure high fidelity regulation of gene expression.