[Tissue specificity of the decrease of cattle lymphocyte DNA methylation during chronic lymphoid leukemia].

It has been found that the content of m5C in the DNA preparations tested have been revealed. The DNAs from normal and leukemic lymphocytes of blood, lymphonodi and spleen differ in ther acceptor ability in the reaction of heterologous methylation in vitro, induced by DNA-methylase from Enterobacter cloacea in the presence of [3H-methyl]S-adenosyl methionine: the ratio of radioactivities in methylated cytosine and adenine residues (m5C/m6A) in leukemic lymphocyte DNA is much lower than in healthy animals' lymphocytes. The decrease in the methylation of DNAs from various lymphoid organs of animals with chronic lymphoid leukemia is well correlated with the impairment. No significant changes of the m5C level and the acceptor ability of the in vitro reaction of heterologous methylation of cow lymph lymphocyte DNA have been observed. The data obtained may be interpreted in terms of tissue (cell) specificity or differences in the degree of DNA methylation under conditions of chronic lymphoid leukemia. It is assumed that the changes in DNA methylation may underlie the disturbances in the regulation of activity of the leukemic cell genetic mechanisms.