SHORT COMMUNICATION Studies on hypomethylation of liver DNA during early stages of

Our finding that the inhibitors of DNA methylation, 5-azacytidine, 5-azadeoxycytidine or adenosine dialdehyde, given after a carcinogen all potentiated initiation suggested that hypomethylation of DNA during repair synthesis of DNA might play a role in the initiation of the carcinogenic process. To examine this aspect further, we have asked the question, do the nodules which develop from initiated cells after promotion with 1 % orotic acid exhibit an altered methyl-ation pattern in their DNA? The methylation status of the DNA from nodules has been examined using the restriction endonucleases HpaWMspl and Hhal which distinguish between methylated and unmethylated cytosines in then* nucleotide recognition DNA 5-CCGG and 5-GCGC respec-tively. The proto-oncogenes, c-myc, c-fos and c-Ha-ras, in the DNA were primarily studied in this investigation because o