Proteins selected for degradation are labeled with multiple molecules of ubiquitin and are subsequently cleaved by the 26 S proteasome. A family of proteins containing at least one ubiquitin-associated (UBA) domain and one ubiquitin-like (UBL) domain have been shown to act as soluble ubiquitin receptors of the 26 S proteasome and introduce a new level of specificity into the degradation system. They bind ubiquitylated proteins via their UBA domains and the 26 S proteasome via their UBL domain and facilitate the contact between substrate and protease. NEDD8 ultimate buster-1 long (NUB1L) belongs to this class of proteins and contains one UBL and three UBA domains. We recently reported that NUB1L interacts with the ubiquitin-like modifier FAT10 and accelerates its degradation and that of its conjugates. Here we show that a deletion mutant of NUB1L lacking the UBL domain is still able to bind FAT10 but not the proteasome and no longer accelerates FAT10 degradation. A version of NUB1L lacking all three UBA domains, on the other hand, looses the ability to bind FAT10 but is still able to interact with the proteasome and accelerates the degradation of FAT10. The degradation of a FAT10 mutant containing only the C-terminal UBL domain is also still accelerated by NUB1L, even though the two proteins do not interact. In addition, we show that FAT10 and either one of its UBL domains alone can interact directly with the 26 S proteasome. We propose that NUB1L not only acts as a linker between the 26 S proteasome and ubiquitin-like proteins, but also as a facilitator of proteasomal degradation. Proteins selected for degradation are labeled with multiple molecules of ubiquitin and are subsequently cleaved by the 26 S proteasome. A family of proteins containing at least one ubiquitin-associated (UBA) domain and one ubiquitin-like (UBL) domain have been shown to act as soluble ubiquitin receptors of the 26 S proteasome and introduce a new level of specificity into the degradation system. They bind ubiquitylated proteins via their UBA domains and the 26 S proteasome via their UBL domain and facilitate the contact between substrate and protease. NEDD8 ultimate buster-1 long (NUB1L) belongs to this class of proteins and contains one UBL and three UBA domains. We recently reported that NUB1L interacts with the ubiquitin-like modifier FAT10 and accelerates its degradation and that of its conjugates. Here we show that a deletion mutant of NUB1L lacking the UBL domain is still able to bind FAT10 but not the proteasome and no longer accelerates FAT10 degradation. A version of NUB1L lacking all three UBA domains, on the other hand, looses the ability to bind FAT10 but is still able to interact with the proteasome and accelerates the degradation of FAT10. The degradation of a FAT10 mutant containing only the C-terminal UBL domain is also still accelerated by NUB1L, even though the two proteins do not interact. In addition, we show that FAT10 and either one of its UBL domains alone can interact directly with the 26 S proteasome. We propose that NUB1L not only acts as a linker between the 26 S proteasome and ubiquitin-like proteins, but also as a facilitator of proteasomal degradation. Ubiquitin, a small protein of 76 amino acids is one of the most conserved proteins known and has been found in all eukaryotic cells studied. It is essential for a variety of cellular processes, including degradation, cell-cycle regulation, DNA repair, stress response, embryogenesis, apoptosis, signal transduction, and transmembrane and vesicular transport (1.Pickart C.M. Annu. Rev. Biochem. 2001; 70: 503-533Crossref PubMed Scopus (2993) Google Scholar, 2.Hicke L. Cell. 2001; 106: 527-530Abstract Full Text Full Text PDF PubMed Scopus (290) Google Scholar, 3.Jesenberger V. Jentsch S. Nat. Rev. Mol. Cell Biol. 2002; 3: 112-121Crossref PubMed Scopus (312) Google Scholar, 4.Lai E.C. Curr. Biol. 2002; 12: R74-R78Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar, 5.Ma Y. Hendershot L.M. Cell. 2001; 107: 827-830Abstract Full Text Full Text PDF PubMed Scopus (357) Google Scholar, 6.Koepp D.M. Harper J.W. Elledge S.J. Cell. 1999; 97: 431-434Abstract Full Text Full Text PDF PubMed Scopus (399) Google Scholar). 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In this we the of the UBL and UBA domains of NUB1L on the and degradation of FAT10 as as the of the two UBL domains of FAT10. We able to show that all three UBA domains of NUB1L are for FAT10 the NUB1L UBL domain with the 26 S proteasome. a NUB1L mutant lacking the UBA domains still able to the degradation of even though the two proteins no longer be by the that FAT10 and NUB1L as as UBL domains of FAT10 with the 26 S proteasome. we found no between the of target proteins to NUB1L and the ability of NUB1L to their degradation, that NUB1L, by to the proteasome via its UBL functions as a facilitator of proteasomal degradation of FAT10 the to as a for in and for the in The for shown in and and A of protein and for the in and for the in for the shown in and a for the in The in and with a The of the proteasome with of of the Biochem. J. PubMed Scopus Google Scholar). The by has been described S. M. G. Mol. Cell. Biol. PubMed Scopus Google Scholar), a E. 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PubMed Scopus Google Scholar). the and C-terminal domains can interact with NUB1L we However, the of UBL proteins that we only in the of proteasome not this we of to the of as we for FAT10 as and as or cells with the either alone or with and to the proteins by and The of this to with to the level of NUB1L As shown in only the UBL domain of FAT10 and no NUB1L signal in cells and cells or the C-terminal UBL domain of FAT10 that the of NUB1L in all to to the NUB1L and the of NUB1L on the of the two UBL domains of we the of degradation of and As can be in A and the degradation of the two UBL proteins in cells with a with that of S. M. G. Mol. Cell. Biol. 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C.M. 2002; PubMed Scopus Google Scholar), is that proteins, which bind to via their UBL can be to target a of ubiquitylated to the proteasome a of Here we the for a proteasomal of the ubiquitin-like protein FAT10 and the protein In we the we the domains of NUB1L and FAT10 for and accelerated of the to to degradation of to to degradation by in a new we NUB1L as a of FAT10 that contains three UBA domains, that are for the with FAT10. the can be as a deletion mutant of NUB1L, to the UBA domains in and We found in and that all three UBA domains of NUB1L for the of the UBL domain for this We able to a of FAT10 and in that the of the two UBA domains can a but this not in in the of this the deletion of the amino acids in the to the to FAT10. the of UBA domains with S. C.M. Nat. Mol. Biol. 12: PubMed Scopus Google the UBA domains into on their ability to between and The members of the which all three UBA domains of NUB1L, not able to interact with ubiquitin at all and be in of ubiquitin-like proteins most domain proteins on ubiquitin or is known their with ubiquitin-like In the three on this and NUB1L found to bind to the ubiquitin-like modifier NEDD8 and to its degradation T. K. T. J. Biol. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, K. Kamitani T. J. Biol. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, T. Kamitani T. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). the of and NEDD8 not by the three UBA domains but by a C-terminal the UBA domain of NUB1L to interact with NEDD8 but not to NEDD8 degradation T. Kamitani T. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). we reported the between FAT10 and NUB1L, but in the of we to of NEDD8 and NUB1L S. M. G. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). In this we found that the of three UBA domains of NUB1L is for the of a ubiquitin-like protein containing two UBL domains. only one or of the UBL domains of FAT10 are for NUB1L, that only the but not the C-terminal UBL domain of FAT10 with NUB1L and of ubiquitin, known to be for the of ubiquitin with other UBA domains S. C.M. J. Mol. Biol. PubMed Scopus Google Scholar, S. J. Mol. Biol. PubMed Scopus Google Scholar, G. M. C. S. A. 1996; PubMed Scopus Google Scholar, C.M. L. J. Biol. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar), are only conserved in FAT10. The UBL domain of FAT10 contains the and a in but a in The C-terminal in the and this to be in with be that be for between NUB1L and ubiquitin-like be shown that NUB1L not bind a protein S. M. G. J. Biol. Full Text Full Text PDF PubMed Scopus Google or S. C.M. Nat. Mol. Biol. 12: PubMed Scopus Google Scholar). of with UBA domain proteins has been reported M. M. M. 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Full Text Full Text PDF PubMed Scopus Google that of the domain of serves to facilitate the degradation of by this for NUB1L and be to the of FAT10 at the 26 S proteasome. the mutant is a protein its ability to interact with the proteasome of can be by of the recently that to the proteasome is to target for proteasomal degradation D.M. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). J. Cell. Full Text Full Text PDF PubMed Scopus Google found that the proteasome substrate to the 26 S in of but no degradation observed. to be a but not a for proteasomal degradation of at least the of or the of their or NUB1L to the proteasome to be We for and for a of 26 S proteasome. and E. are for the of
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