title: Involvement of deoxyribonuclease activity in the differential sedimentation rates of nucleoids from non-transformed and transformed mouse embryo fibroblasts.
abstract: Lysis of non-transformed confluent C3H10T1/2C18 mouse embryo fibroblasts in the presence of detergents, high concentrations of salt and EDTA on top of neutral sucrose gradients revealed a reduced sedimentation rate of the resulting nucleoids from these cells compared to those from exponentially growing non-transformed cells or from transformed cells. Exposure of confluent cells to 1000 rads of X-ray had no effect on this rate of nucleoid sedimentation; and ethidium bromide titration and alkaline sucrose analysis suggested the presence of discontinuities in the DNA. An endonucleolytic activity could be extracted from nuclei of these cells with 0.5 M NaCl, indicating a very tight association with the chromatin. Such an enzyme in non-transformed confluent cells may account for the differences in nucleoid structure and may be related to changes in cell function with normal arrest of cell growth. There was no growth-phase effect on the properties of nucleoids from transformed cells.
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000032:analysis / Q000201:enzymology*; D002471:Cell Transformation, Neoplastic / Q000032:analysis*; D002499:Centrifugation, Density Gradient; D004278:DNA, Superhelical / Q000032:analysis*; D003851:Deoxyribonucleases / Q000032:analysis*; D004587:Electrophoresis, Agar Gel; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000201:enzymology; D051379:Mice; D008809:Mice, Inbred C3H
chemical_list: D004278:DNA, Superhelical; D003851:Deoxyribonucleases