Pattern of methylation of two genes coding for housekeeping functions.

Abstract

The distribution of sites that can be methylated was analyzed in the Chinese hamster adenine phosphoribosyltransferase (aprt) gene and the patterns of methylation of this gene and the mouse dihydrofolate reductase (dhfr) gene were studied by using CpG restriction enzymes. Both genes were found to be unmethylated completely at their 5''-end region and methylated heavily throughout the rest of the gene. Because the hamster aprt gene can be inhibited by DNA methylation in vivo, the results suggest that 5'' undermethylation of this gene may be a necessary condition for its expression. The pattern of methylation of each of these 2 genes was similar in sperm and all other somatic tissue DNA. This is in contrast to many tissue-specific genes that were found to be highly methylated in sperm DNA and undermethylated in the tissue in which they are expressed. Both aprt and dhfr are key enzymes in the biosynthesis of nucleotides and therefore expected to be synthesized in all cells.