9ndp

Structural highlights

Function

RS27A_RABIT 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 proteotoxic stress response and cell cycle; 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.[UniProtKB:P62979] Component of the 40S subunit of the ribosome (PubMed:23873042, PubMed:25601755, PubMed:27863242, PubMed:30517857). Part of the small subunit (SSU) processome, first precursor of the small eukaryotic ribosomal subunit (PubMed:23873042, PubMed:25601755, PubMed:27863242, PubMed:30517857). During the assembly of the SSU processome in the nucleolus, many ribosome biogenesis factors, an RNA chaperone and ribosomal proteins associate with the nascent pre-rRNA and work in concert to generate RNA folding, modifications, rearrangements and cleavage as well as targeted degradation of pre-ribosomal RNA by the RNA exosome (PubMed:23873042, PubMed:25601755, PubMed:27863242, PubMed:30517857).^{[1] [2] [3] [4]}

References

1. ↑ Lomakin IB, Steitz TA. The initiation of mammalian protein synthesis and mRNA scanning mechanism. Nature. 2013 Jul 21. doi: 10.1038/nature12355. PMID:23873042 doi:10.1038/nature12355
2. ↑ Muhs M, Hilal T, Mielke T, Skabkin MA, Sanbonmatsu KY, Pestova TV, Spahn CM. Cryo-EM of Ribosomal 80S Complexes with Termination Factors Reveals the Translocated Cricket Paralysis Virus IRES. Mol Cell. 2015 Feb 5;57(3):422-432. doi: 10.1016/j.molcel.2014.12.016. Epub 2015 , Jan 15. PMID:25601755 doi:http://dx.doi.org/10.1016/j.molcel.2014.12.016
3. ↑ Shao S, Murray J, Brown A, Taunton J, Ramakrishnan V, Hegde RS. Decoding Mammalian Ribosome-mRNA States by Translational GTPase Complexes. Cell. 2016 Nov 17;167(5):1229-1240.e15. doi: 10.1016/j.cell.2016.10.046. PMID:27863242 doi:http://dx.doi.org/10.1016/j.cell.2016.10.046
4. ↑ Flis J, Holm M, Rundlet EJ, Loerke J, Hilal T, Dabrowski M, Burger J, Mielke T, Blanchard SC, Spahn CMT, Budkevich TV. tRNA Translocation by the Eukaryotic 80S Ribosome and the Impact of GTP Hydrolysis. Cell Rep. 2018 Dec 4;25(10):2676-2688.e7. doi: 10.1016/j.celrep.2018.11.040. PMID:30517857 doi:http://dx.doi.org/10.1016/j.celrep.2018.11.040
5. ↑ Zdancewicz S, Maldosevic E, Malezyna K, Jomaa A. NAC couples protein synthesis with nascent polypeptide myristoylation on the ribosome. EMBO J. 2025 Aug 26. PMID:40859030 doi:10.1038/s44318-025-00548-4