DNA METHYLASES FROM HUMAN THYROID NODULAR AND DIFFUSE GOITERS

Heterogeneity and some properties of DNA methylases isolated from nonm alignant human thyroid nodular and diffuse goiters (NG and DG, respect ively) were investigated. Six or seven distinct active fractions were detected in preparations of DNA methylases by isoelectric focusing; th e fi actions were different in isoelectric point (pI), degree of activ ation by Ca2+ and Mg2+, sensitivity to dithiothreitol, and ability to methylate cytosine residues in DNA mono-, di, and tri-pyrimidine seque nces to form 5-methylcytosine residues in vitro. The degree of methyla tion of homologous DNA in vivo depended on the goiters. Analysis of se veral DNA methylase fractions by two-dimensional electrophoresis by O' Farrell's method showed the presence of polypeptides of similar molecu lar weight (about 36 kD) as the dominant component. In addition, all D NA methylase preparations analyzed contained 6 or 7 specific minor com ponents. Thus, the data show possible structural and functional hetero geneity of human DNA methylases.