Ubiquitin-Proteasome Pathway (UPP)
Protein homeostasis at the cellular level is precisely balanced by de-novo synthesis, post-translational modifications and proteolytic degradation. Protein degradation serves several functions including the elimination of damaged and no longer needed proteins, activation of protein precursors by partial hydrolysis or the complete hydrolysis of proteins that regulate multiple functions. The majority (>80%) of all mammalian proteins are degraded by the ubiquitin proteasome system (UPS). Over the past decade, knowledge about the UPS has exploded. It has now become obvious that the ubiquitination of proteins does not solely target them for degradation, but can also play a role in regulatory functions including translational regulation, activation of transcription factors and kinases, DNA repair, endocystosis and vesicular transport of membrane proteins.
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