Figure 4. Rapid degradation of premature translational termination products.

A. Denaturing immunoprecipitation of peptidyl-puromycins. 293-K^b cells were radiolabeled for 30 minutes with [³⁵S]-Met, 20 µM puromycin, and 20 µM MG132. Polypeptides were precipitated with TCA, solubilized, then subjected to a denaturing immunoprecipitation using either non-specific rabbit serum (negative IP control) or anti-puromycin serum. Results are representative of three independent experiments. B. 293-K^b cells were pulse labeled with [³⁵S]-Met and 20 µM puro and chased as described in Fig. 3B. Solubilized TCA precipitates were subjected to denaturing immunoprecipitation using anti-puromycin serum. [³⁵S] in the anti-puromycin immunoprecipitates was measured by liquid scintillation counting (n = 4; mean ± s.e.m.).