[On the impossibility of the incorporation of 5-methylcytosine and its nucleosides into higher plant DNA].

No radioactivity was detected in 5-methylcytosine isolated from wheat DNA after incubation of wheat seedlings with 3H-labelled 5-methylcytosine, 5-methylcytidine and 5-methyldeoxycytidine. No label from 3H-5-methylcytosine was found in DNA of seedlings. After incubation of seedlings with 3H-labelled nucleosides of 5-methylcytosine, radioactivity was discovered only in thymine of DNA. Thus 5-methylcytosine and its nucleosides can not be used in plants as direct precursors of 5-methyl cytosine residues in DNA, but nucleosides of 5-methylcytosine may be deaminated to thymidine (or deoxythymidine) and subsequently incorporated into DNA.