The nature of DNA synthesized in nuclei from mouse L1210 cells

A reassessment of the mechanism of action of 4'-[(9-acridinyl)-amino]methanesulphon-m-anisidide

The conclusion that treating cells with 4'-[(9-acridinyl)- amino]methanesulphon-m-anisidide (mAMSA) causes an alkali-dependent decrease in the size of their DNA was reinvestigated. Evidence is presented that alkali is not needed to detect an effect of mAMSA on the sedimentation rate of DNA released from mAMSA-treated PY815 cells and that mAMSA causes double-strand breaks in cellular DNA.

Effect of Ehrlich ascites cell chalone on nascent DNA synthesis in isolated nuclei

Ehrlich Ascites Tumor (EAT) chalone has been shown to inhibit nascent DNA synthesis by inhibiting DNA polymerase alpha and beta (Nakai, 1976), but one of the problems in studying eurkaryotic DNA replication has been the relative impermeability of the cell membrane to precursors and macromolecules; hence, to circumvent this restriction without sacrificing the integrity of the replication process, a broken cell system utilizing nuclei in aqueous media was investigated. Isolated nuclei appear to continue the process of DNA replication that was proceeding in vivo before their isolation and under optimal concitions are able to initiate new synthesis (Fraser & Huberman, 1977). The effects of partially purified EAT chalone on nascent DNA could be studied directly in this nuclear system, which excluded effects of the cell membrane, nucleotide pools and other cytosol elements. A concentration-related inhibition of [3H]thymidine triphosphate ([3H]dTTP) incorporation was noted over a chalone range of 50-200 micrograms/ml. It appears that chalone can inhibit DNA polymerase alpha directly within the nucleus without an intermediate step such as a cell membrane receptor.