Table 1.

Cyclin D1 half-life in NIH-3T3 fibroblasts

Treatment	D1 t (min)
Proliferating in serum-containing medium	24 ± 4
Wortmannin (100 nm) plus complete medium	10 ± 2
Induced MEK1 (serum starved)	11 ± 2
RasV12 transfected (serum starved)	31 ± 7
RasV12.S35 transfected (serum starved)	14 ± 2
D1 overexpression (serum starved)	13 ± 2

NIH-3T3 cells proliferating in the presence of serum or derivatives modified as indicated were labeled with l-[³⁵S]methionine for 30 min and chased in the presence of excess unlabeled precursor. Radiolabeled cyclin D1 was precipitated from lysates collected after 0, 5, 10, 20, 40, 80, and 120 min using a D1-specific monoclonal antibody. Proteins were resolved on denaturing gels, detected by autoradiography, and the relative amount of radiolabeled cyclin D1 at each time point was determined by densitometric scanning of the film. The mean half-life of cyclin D1 (±s.d. from the mean) determined for each cell line was calculated from three to five independent experiments.