DNA-synthesis and DNA-methylation in the spleen of immunized mice.

Methylation of spleen DNA was investigated in mice immunized with bovine serum albumin. At the time of the highest incorporation of deoxythymidine into DNA -24 hours after antigen application--there is an elevated DNA methylation rate as shown by the transfer of the methyl group of methionine to DNA cytosine as well as by the conversion of DNA cytosine to DNA 5-methyl-cytosine. There is no difference in the methylation rate between bulk DNA and satellite DNA.