TABLE 3.

Transfection of Cdk2-dn in serum-starved and restimulated 3T3 cells blocks DNA condensation after BrdU incorporation^a

Ratio of expression plasmid to marker plasmid	BrdU-positive nuclei with condensed DNA (%)b
	Vector	Cdk2-dn
1:1	77 ± 1	53 ± 9
2:1	75 ± 5	39 ± 4
4:1	78 ± 2	28 ± 1

^a3T3 cells were synchronized by serum starvation, restimulated with serum (0 h), and cotransfected (between 4 h and 10 h) with a plasmid expressing β-Gal and either an empty vector or one expressing Cdk2-dn. BrdU was added at 10 and 24 h, to ensure continuous labeling of cells in DNA synthesis. Nocodazole was added at 32 h and washed off at 48 h. The cells were fixed at 50 h. A least 100 β-Gal- and BrdU-positive cells were scored for each condition, to determine the fraction with condensed DNA (stained with bisbenzimide). 

^bMeans ± standard deviation from four independent experiments for the 2:1 ratio; mean ± range from two independent experiments for the 1:1 and 4:1 ratios.