Ubiquitin (UBB) Recombinant Protein

This gene encodes ubiquitin, one of the most conserved proteins known. Ubiquitin has a major role in targeting cellular proteins for degradation by the 26S proteosome. It is also involved in the maintenance of chromatin structure, the regulation of gene expression, and the stress response. Ubiquitin is synthesized as a precursor protein consisting of either polyubiquitin chains or a single ubiquitin moiety fused to an unrelated protein. This gene consists of three direct repeats of the ubiquitin coding sequence with no spacer sequence. Consequently, the protein is expressed as a polyubiquitin precursor with a final amino acid after the last repeat. An aberrant form of this protein has been detected in patients with Alzheimer's disease and Down syndrome. Pseudogenes of this gene are located on chromosomes 1, 2, 13, and 17. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Aug 2013]

Function: 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. Ref.8 Ref.12

Subcellular location: Ubiquitin: Cytoplasm

By similarity. Nucleus

By similarity.

Miscellaneous: Ubiquitin is encoded by 4 different genes. UBA52 and RPS27A genes code for a single copy of ubiquitin fused to the ribosomal proteins L40 and S27a, respectively. UBB and UBC genes code for a polyubiquitin precursor with exact head to tail repeats, the number of repeats differ between species and strains.The mRNA encoding variant UBB(+1) is produced by an unknown mechanism involving the deletion of a GT dinucleotide in the close proximity of a GAGAG motif (Ref.14). This variant mRNA is found in normal brain, but the encoded protein accumulates only in brain neurofibrillary tangles and neuritic plaques in Alzheimer disease and other tauopathies, as well as polyglutaminopathies (Ref.15). UBB(+1) variant cannot be used for polyubiquitination, is not effectively degraded by the proteasome when ubiquitinated and ubiquitinated UBB(+1) is refractory to disassembly by deubiquitinating enzymes (DUBs). In healthy brain, UBB(+1) C-terminus can be cleaved by UCHL3 (Ref.13).For a better understanding, features related to ubiquitin are only indicated for the first chain.

Sequence similarities: Belongs to the ubiquitin family.Contains 3 ubiquitin-like domains.