DNA Ligase and DNase Activities in Mouse Erythroleukemia Cells During Dimethyl Sulfoxide-induced Differentiation

DNA ligase and DNase levels were measured in cell-free extracts from untreated mouse erythroleukemia (MEL) cells and from cells treated with dimethyl sulfoxide (Me₂SO) to induce erythroid differentiation. The DNase activity present in the extracts was sensitive to inhibition by G-actin and was, therefore, presumed to be DNase I. When the MEL cells were induced to differentiate by culturing in the presence of 1.8% Me₂SO for 3 or 4 days, the apparent activity of the DNA ligase decreased to approximately 12% of the value in untreated MEL cells. In contrast, the apparent DNase I activity of the extracts from Me₂SO-treated cells increased over that in extracts from untreated cells by a factor of 2. The activity of acid phosphatase, a lysosomal enzyme, remained unchanged. When strain DR-10, a mutant of the MEL cells which does not undergo Me₂SO-induced differentiation, was treated with Me₂SO, the DNA ligase and DNase activities of extracts from these cells remained unchanged as compared to extracts from untreated DR-10 cells. Therefore, the marked decrease in the level of DNA ligase activity appeared to be related to the process of differentiation in the Me₂SO-treated MEL cells.