摘要：

A particle-free extract has been prepared from Ehrlich ascites tumour cells disrupted sonically or osmotically which promotes the incorporation of [ 3H]thymidine into DNA in the presence of ATP, Mg ++ ions and carrier DNA. With sonic extracts glucose and DPN in high concentrarions are required for good incorporation; with osmotic extracts a low concentration of DPN suffices. Incorporation is diminished by dialysis and is promoted by low concentrations of deoxyribonucleoside monophosphates and to a greater extent by deoxyribonucleoside triphosphates. Evidence is presented that incorporation is preceded by conversion of [ 3H]TDR to [ 3H]TTP. Degradation of the [ 3H]DNA yields among other products [ 3H]thymidine diphosphate. Investigation of extracts from a series of different tissues shows that ability to incorporate [ 3H]TDR into DNA is greater in tissues of high mitotic activity.

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