Quantitating defective ribosome products.

The fidelity of the protein production process is monitored by quality control machinery, which ensures that aberrant proteins are not deployed throughout the cell. A significant fraction (upwards of 30%) of proteins are degraded by proteasomes shortly after their synthesis, and we have termed such proteins defective ribosomal proteins (DRiPs). It is of interest and importance to characterize qualitatively and quantitatively this cohort of rapidly degraded nascent proteins. Quantitating DRiPs entails employing a standard pulse-chase protocol using radiolabeled amino acids. Protein degradation kinetics can be determined by either acid precipitation or SDS-PAGE. The introduction of proteasome inhibitors enables quantitation of proteasome-mediated protein degradation in vivo.