Methylation of DNA in developing sea urchin embryos.

Abstract

The methylation of DNA in developing sea urchin embryos has been studied. 5-methylcytosine is the only “minor” base found in DNA of sea urchin embryos at all stages of the early embryonic development. The occurrence of other methylated bases up to a level of 1/20 of 5-methylcytosine can be excluded. The methyl group of methionine is transferred onto specific DNA cytosines. The distribution of 5-methylcytosine on DNA is non-random: about 60% of total 5-methylcytosine was found in the monopyrimidine fraction of the DNA pyrimidine isostichs. In addition 90% of 5-methylcytosine was found in the dinucleotide (CG) separated from a DNase digest. The data suggest that DNA 5-methylcytosine is synthesized at the polymer level in developing sea urchin embryos as it is known to occur in other organisms. Experiments which indicate an active transport for l-methionine and l-serine by developing sea urchin embryos are also reported.