SYNTHESIS OF RNA IN MAMMALIAN CELLS DURING MITOSIS AND INTERPHASE

Chinese hamster cells in the mitotic and G1 phases of the growth cycle were incubated for 30 or 60 min in suspension tissue culture and pulse-labeled with tritiated uridine. After ap-propriate chases, washes, and extractions, it was found that all in-corporation into the nucleic acid may be accounted for by those cells in interphase. An average of 410 counts was found for incorpora-tion into the cell population (approximately 2.0 x 105 cells) of which over 80% of the cells was initially in mitosis. The increasing number of cells leaving mitosis and entering interphase during the 30 min incubation was theoretically able to account for 470 counts. In addition, short-pulse labeling experiments have shown a consistent linear relationship between the percentage of cells in division and the in-corporation of the isotope, which strongly suggests that, if 100% of the cells were in mitosis, the counts would be essentially zero. Thus, the entire label may be attributed to those cells in interphase where portions of the chromosomal material are known to be already extended.