Tissue-specific hypomethylation of the human c-K-ras gene.

Methylation of the c-K-ras gene was examined in a wide variety of human tissues using the methylation sensitive restriction endonuclease HpaII. All tissues showed hypomethylation in the region of exon zero. Specific hypomethylation of a particular HpaII site in the second intron was observed in gastrointestinal and tracheobronchial epithelial cell DNAs. Specific hypomethylation was also observed in a cluster of HpaII sites within the first intron in sperm, endometrium and placenta DNAs. These regions were predominantly methylated in a wide variety of other tissues, including fetal gut. The possible implications are discussed.