Protein degradation breaks proteins into smaller products and helps control protein abundance and quality. The ubiquitin-proteasome system selectively targets many intracellular proteins, while lysosomes degrade other material delivered by intracellular trafficking or autophagy. Synthesis and removal jointly determine abundance, so reduced protein level need not imply reduced transcription. Controlled degradation also makes some regulatory changes rapid and effectively irreversible for the individual protein molecule. [ref]
Rapid removal of an existing protein pool to separate immediate effects from later adaptation. Depletion kinetics and perturbation specificity need direct measurement.
