Rao P N, Sunkara P S, Wilson B A
Proc Natl Acad Sci U S A. 1977 Jul;74(7):2869-73. doi: 10.1073/pnas.74.7.2869.
The object of this study was to determine whether the inducer(s) of DNA synthesis in mammalian cells accumulates gradually throughout the G1 period or becomes available suddenly at the G1-S transition. HeLa cells, synchronized at various points in the G1 period, were fused by using UV-inactivated Sendai virus. Early G1 cells were fused with mid-G1 or late G1 cells and late G1 cells were fused with mid-G1 cells. The G1 traverse of mono-, bi-, and trinucleated cells was studied. The bi- and trinucleated cells of mid-G1 and late G1 parents traversed the G1 period significantly faster than did their mononucleated counterparts. The reduction in the duration of the G1 period was proportional to the number and age of nuclei at the time of fusion. There was no significant difference between the mono- and binucleated cells of the early G1 parent in their rates of entry into S period. In light of these findings, a model is proposed in which the inducer(s) of DNA synthesis accumulates gradually throughout the G1 period, reaching a critical level at the G1-S boundary when DNA replication is initiated; after reaching a peak during early or mid-S period, it declines to below the critical level when DNA synthesis ceases.
本研究的目的是确定哺乳动物细胞中DNA合成诱导物是在整个G1期逐渐积累，还是在G1-S转换点突然出现。通过使用紫外线灭活的仙台病毒，将在G1期不同时间点同步化的HeLa细胞进行融合。将早期G1细胞与中期G1或晚期G1细胞融合，以及将晚期G1细胞与中期G1细胞融合。研究了单核、双核和三核细胞的G1期进程。中期G1和晚期G1亲本的双核和三核细胞穿越G1期的速度明显快于它们的单核对应细胞。G1期持续时间的缩短与融合时细胞核的数量和年龄成正比。早期G1亲本的单核和双核细胞进入S期的速率没有显著差异。根据这些发现，提出了一个模型，其中DNA合成诱导物在整个G1期逐渐积累，在启动DNA复制的G1-S边界达到临界水平；在S期早期或中期达到峰值后，当DNA合成停止时，它下降到临界水平以下。
