[Some peculiarities of pyrimidine isoplyth methylation of newly synthesized DNA from human blood lymphocytes in normal conditions and chronic lymphoycytic leukemia].

Methylation of pyrimidine isoplythes of newly synthesized DNA from activated human blood lymphocytes was studied under normal conditions and in chronic lymphocytic leukemia. The analysis of distribution of labelled 5-methylcytosine in DNA pyrimidine oligonucleotides, differing in their lengths, showed a considerable increase in the methylation of pyrimidine oligonucleotide fragments of DNA from lymphocytic leukemia lymphocytes as compared to normal. The greatest differences were observed in methylation with respect to longer fragments, e.g. under chronic lymphocytic leukemia the level of methylation of the cytosine residues of DNA in isoplythes I and II, as well as in the fraction of isoplyth III and in longer fragments exceeded that of the normal DNA isoplythes, 3.7-, 2.1- and 8.3-fold respectively.