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Poly(Adenosine Diphosphate Ribose) Synthesis during the Cell Cycle of Transformed Hamster Lung Cells¹

Department of Molecular Oncology, The Institute of Medical Science, Tokyo University, P.O. Takanawa [M. M., T. S.], and Department of Experimental Pathology, Cancer Institute, Nishi-Sugamo, Toshima-ku, Tokyo, Japan [N. I., S. T.]

Poly(adenosine diphosphate ribose) synthesis from ³H-labeled nicotinamide adenine dinucleotide during the cell cycle of highly synchronized, transformed hamster lung cells was studied by autoradiography and enzymatic assay.

In the G₂ phase, 70% of the cells were labeled and the average grain number was 69 per nucleus. In the M and late-S phases, only 5 and 12%, respectively, of the cells were labeled. There was a second peak of incorporation of radioactivity in the G₁ phase, in which 31% of the cells were labeled.

Enzymatic assay showed that the specific activity of poly(adenosine diphosphate ribose) polymerase of isolated nuclei was highest in the G₂ phase and lowest in the S phase.

In telophase, silver grains were localized exclusively over the cytoplasm and no grains were observed over the nuclei, while silver grains were localized only over the nuclei in the G₁ and G₂ phases.

¹ This work was supported by grants from the Ministry of Education, Japan, and the Wachsman Foundation.

Received 12/19/72. Accepted 3/ 9/73.