title: Non-random distribution of N-methyl-N-nitrosourea sensitive sites in a eukaryotic genome.
abstract: DNA released from Ehrlich ascites cells by lysis in the presence of 50 microgram X ml-1 of proteinase K contains long alkali-stable strands in the order of 50-100 X 10(6) daltons. In contrast, DNA released in the presence of 6 mg X ml-1 of autodigested pronase is significantly nicked. According to sedimentation rates the number of internal ends liberated during this procedure is 24/200 X 10(6) daltons. The number of alkali-labile sites introduced into DNA by incubation of Ehrlich ascites cells with 1 nM of N-methyl-N-nitrosourea (MNU) followed by cell lysis in the presence of 50 microgram X ml-1 of proteinase K and alkali-denaturation is 16.6/200 X 10(6) daltons. From this one should expect that denatured DNA released from cells pretreated with 1 mM of MNU which are subsequently lysed with 6 mg X ml-1 of pronase would have about 40 single-strand breaks/200 X 10(6) daltons. However, denatured DNA strands released by 6 mg X ml-1 of pronase either from MNU-treated or untreated cells cannot be separated by centrifugation through alkaline sucrose gradients. This phenomenon could be explained by a non-random distribution of MNU-inducible alkali-labile sites of DNA in vivo.
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000032:analysis*; D002499:Centrifugation, Density Gradient; D004273:DNA, Neoplasm / Q000302:isolation & purification*; D019286:Endopeptidase K; D010450:Endopeptidases / Q000378:metabolism; D008770:Methylnitrosourea / Q000494:pharmacology*; D009607:Nitrosourea Compounds / Q000494:pharmacology*; D009691:Nucleic Acid Denaturation
chemical_list: D004273:DNA, Neoplasm; D009607:Nitrosourea Compounds; D008770:Methylnitrosourea; D010450:Endopeptidases; D019286:Endopeptidase K