DNA polymerase activities during induced differentiation in murine erythroleukemia cells

Abstract

DNA polymerase activities with properties similar to those described for other eukaryotic cells were measured in murine erythroleukemia cells (MELC). Counter-current centrifugation was employed to obtain populations of cells synchronized in different stages of the cell cycle. Alpha DNA polymerase activity, the major DNA polymerase activity in the cell, varies with stage of cell cycle, attaining the highest values in S (DNA synthesis) phase both in differentiating and non-differentiating MELC. When MELC are induced to differentiate by culture with hexamethylene bisacetamide (HMBA) the observed alteration in progression through the cell cycle is reflected in α DNA polymerase activity. Induced cells, delayed in G1, have a low level of α DNA polymerase activity, characteristic of G1 cells, but α activity increases when cells re-enter S phase. MELC induced to differentiate undergo a limited number of cell divisions and then lose the ability to divide. Terminal cell division is accompanied both by a loss of the ability to incorporate labelled thymidine into DNA and by a marked decrease in α DNA polymerase activity. No significant differences in β DNA polymerase activity were detected either in different stages of the cell cycle or during terminal differentiation.