Ubiquitin: exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in lysosomal degradation; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling.
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Protein Aliases: 60S ribosomal protein L40; CEP52; HUBCEP52; L40; Large ribosomal subunit protein eL40; RPL40; Ubiquitin; Ubiquitin A-52 residue ribosomal protein fusion product 1; ubiquitin carboxyl extension protein 52; ubiquitin-52 amino acid fusion protein; Ubiquitin-60S ribosomal protein L40; ubiquitin-CEP52
Gene Aliases: CEP52; HUBCEP52; L40; RPL40; UBA52; UBCEP2
UniProt ID: (Human) P62987
Entrez Gene ID: (Human) 7311