The role of the G1 period in the life cycle of eukaryotic cells

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Abstract
The objective of this study was to test the concept that the G1 period lacks any specific function in the life cycle of mammalian cells and hence could be drastically reduced without any effect on the generation time. HeLa cells were grown in medium containing an optimum dose (60 μM) of hydroxyurea at which the duration of S period was prolonged with little or no increase in generation time. At this concentration of hydroxyurea, we observed a maximum of 3 h (or 28.5%) reduction in the G1 period. We also studied the effects of synchronization in S phase by single and double thymidine blocks on cell size and its relationship to the duration of G1 in the subsequent cycle. By these treatments, we could reduce the G1 period by not more than 2 to 3 h. The reduction in G1 period was not directly proportional to the size (volume) of the G1 cells. These results suggest that G1 period has certain specific functions and cannot be eliminated by alterations in culture conditions.