| Abstract: | Chinese hamster ovary cells were synchronized by the mitotic selection technique and followed through 3 cell cycles. The maintenance of the observed high degree of synchrony, which would require a standard deviation in generation times of about 10%, could be partially attributed to the influence that S phase cells have on inducing G1 cells to initiate DNA synthesis. In fact, observations using two populations of synchronous cells revealed that conditioned medium collected from synchronous cells in the process of initiating DNA synthesis and/or the close proximity (within 15–100 μm) of S phase cells to G l cells accelerates (by 1.5 to 2.5 h) the entry of G1 cells into S. Thus, when synchronous cells are plated, the presence of cells entering S first could both shorten the average length of G 1 and sharpen synchrony by reducing the time required for the population of G 1 cells to cross the G 1/S boundary. |
