The ubiquitin-proteasome system is a major pathway for protein degradation in cells. Proteins destined for degradation are tagged with ubiquitin, a small regulatory protein, through a series of enzymatic reactions involving ubiquitin-activating, conjugating, and ligase enzymes. The ubiquitin-tagged proteins are then recognized and degraded by the proteasome, a large protease complex, into small peptides, recycling amino acids for new protein synthesis.
