To determine whether methylation changes in specific DNA sequences of the albumin and AFP genes are implicated in the modulation of transcriptional activity during rat liver development and neoplasia we have analysed the methylation pattern of C-C-G-G sequences within these genes in DNA isolated from fetal and adult hepatocytes, from adult kidney and from a clonal hepatoma cell line which produces AFP but no albumin. We have assayed for methylation of the internal cytosine of this sequence by using the restriction enzyme isoschizomers HpaII and MspI. 32P-labelled cloned cDNA probes were used to reveal the albumin and AFP gene containing fragments. Genomic subclones of the albumin gene were also utilized as molecular probes to measure quantitatively the level of methylation of 6 specific sites within the albumin gene in the different DNA samples. The results indicate that methylation changes at the sites analysed are not responsible for the changes in gene activity during rat liver development. Further they demonstrate that: 1) extensively methylated genes can be actively transcribed; 2) prominent changes in methylation of specific genes during normal development are not necessarily related to alterations in gene activity.

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