Make it or break it: the role of ubiquitin-dependent proteolysis in cellular regulation.

Effective regulation of the concentration of a protein in the cell requires rapid protein degradation. Until recently, it was widely believed that intracellular proteolysis was largely confined to the turnover of damaged, or otherwise abnormal, proteins. Recently, however, the role of protein degradation in cellular regulation has gained centre stage, and ubiquitin/proteasome-dependent proteolysis has been shown to play a key role in processes as diverse as embryonic development, transcription and the cell cycle.