本文比较了不同年龄的鼠肝ＤＮＡ甲基化酶活力及ＤＮＡ甲基化水平，发现它们均与鼠龄呈反相关。又以不同年龄的鼠肝ＤＮＡ为模板，检验了其体外转录活力，发现其与鼠龄呈正相关。

The DNA methylation of rat liver during aging process has been studied. Using incorporation of 3 H-labeled methyl group of SAM into DNA bases as a measure,there appears a decreased activity of DNA methylase with the increased age of the rats.Meanwhile ,by means of HPLC, we also found the similar law in the 5-methylcytosine(5mC) content of DNA from rat liver. These results suggest that the decline in 5mC content may be the result of the decreased activity of DNA methylase. With the years,such undermethylation will become increasingly apparent and may well contribute to the aging process. By using these DNA with different methylation level as templates, we assayed the activities of endogenous RNA polymerase and E. coli RNA polymerase in vitro. We found that there is a significantly reverse correlation between the transcriptional level of these DNA and their methylation level. The result provides some theoretical bases for explaining the aging process in the point of gene regulation.