title: [Methylation of newly synthesized DNA in mouse fibroblast culture].
abstract: After a 10 min- or more prolonged incubation of transformed mouse fibroblasts (L.-cells) with [3H]-thymidine or [3H-methyl]-methionine and a subsequent centrifugation of cell lysates in an alkaline sucrose gradient the DNA radioactivity is detected in long (28, 33 and 45S) and short (5, 13 and 18S) fragments. An increase in cell concentration in the cultural layer results in inhibition of 5S fragments linkage rather than in inhibition of their synthesis. The blocking of the Okazaki fragment linkage may be regarded as one of the inhibitory molecular mechanisms of cell depletion. Both in the case of normal and suppressed (by 99%) replication by arabofuranosylcytosine [3H]-thymidine and [3H-5-methyl] cytosine are detected in the Okazaki fragments (5S) as well as in some discrete lower molecular weight fractions (lesser than 5S) of newly synthesized DNA. Thus, replicative methylation of DNA in the fibroblasts occurs in the replicative fork during DNA synthesis and the functioning DNA methylase is an indispensable component of the replicative complex. The methylation of Okazaki fragments is non-chaotic and has a specificity other than that of total DNA. This may be due to the multiplicity and different specificity of nuclear DNA-methylases. Thus, there exist in animal cells replicative and post-replicative methylation of DNA, which may differ in the nature of substrates and enzymes, in specificity of recognizable sequences and in their functional significanse.
mesh_terms: D000818:Animals; D003596:Cytosine / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D007739:L Cells / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D008745:Methylation; D051379:Mice; D013936:Thymidine / Q000378:metabolism
chemical_list: D003596:Cytosine; D004247:DNA; D008715:Methionine; D004248:DNA (Cytosine-5-)-Methyltransferases; D013936:Thymidine
vernacular_title: Metilirovanie vnov' sinteziruemoĭ DNK v kul'ture myshinykh fibroblastov.