FIG. 4.

The absence of p130 form 3 in 293 cells is not due to E1A-mediated selective degradation of this p130 form through the proteasome pathway. 293 cells were grown for the indicated periods of time in DMEM–10% FBS containing 1 μM β-lactone (an inhibitor of the proteasome pathway). β-Lactone was dissolved at the appropriate concentration in DMSO (vehicle), and 15 μl of solution was added per plate. Control cells received 15 μl of DMSO. Cells were collected at the indicated times, and the levels and phosphorylation status of endogenous p130 were determined by Western blot analysis.