[Intragenome distribution of 5-methyl cytosine and reassociation kinetics of cow blood lymphocyte DNA under normal conditions and in chronic lymphoid leukemia].

The DNA from cow blood lymphocytes is methylated in a varying degree: the maximal content of 5-methyl cytosine (2,3 mol%) is found in the "instantly" renaturating sequences (Cot lett than 10(-4)), a relatively large amount (1,4 mol%)--in moderately repeated sequences (Cot = 10(-4)--400) and the minimal amount (0,9 mol%) in the unique sequences (Cot greater than 400). In their reassociation kinetics, GC-content and other physico-chemical properties the blood lymphocyte DNA of the controls and of animals with chronic lymphoid leukemia appear to be similar. Consequently, the genome organization of leukemic animals does not change significantly; a considerable decrease of 5-methyl cytosine of lymphocyte DNA in lymphoid leukemia parallels the decrease of genome methylation in the leukemic cells. This decrease does not affect the unique sequences, but involves all types of repeated sequences (moderately and frequently repeated ones and palindromes). It is assumed that the specific disturbances in genome methylation under lymphoid leukemia may be a cause of transcription deficiences and cell transformations.