[Effect of aflatoxin B1 on DNA enzymatic methylation and secondary structures of the rat liver].

Methylation and secondary structure of DNA in rat liver versus time of aflatoxin B1 (AfB1) treatment were studied. A 50% drop in 5-methylcytosine level in liver DNA as compared with control was observed long before tumor development. Also, certain changes in DNA secondary structure were seen.

[Changes in the structure of DNA induced by sarcolysine in vivo and in vitro].

Secondary structure and the rate of methylation of DNA, isolated from normal and malignant liver tissues (sarcoma 45) were studied in vivo and in vitro in presence of sarcolysine. The differential melting curve (DMC) in the DNA from malignant tissue was shifted, compared with that of the liver DNA, to the low temperature side and was characterized by appearance of an additional peak in the region of 50-60 degrees. A considerable increase in the level of methylation has been also noted in the DNA from malignant tissue.

[Modification of DNA-specific methylation in tissues of healthy and tumor bearing (sarcoma 45) rats under the effect of an active alkylating cancerolytic agent].

The content of 5-methyl cytosine (5-MC) in the DNA preparations from organs and tissues of healthy and tumour-bearing (sarcoma 45) rats and the effect of an alkylating cancerolytic agent on DNA methylation in vivo were studied. The 5-MC content in the DNA preparations from liver, spleen and testicles of tumour-bearing rats and tumour cells was increased, the maximal increase being observed in liver and spleen DNAs (1,71 and 1,70 mol.%, respectively) and in sarcoma DNA (1,93 mol.