title: U box proteins as a new family of ubiquitin-protein ligases.
abstract: The U box is a domain of approximately 70 amino acids that is present in proteins from yeast to humans. The prototype U box protein, yeast Ufd2, was identified as a ubiquitin chain assembly factor that cooperates with a ubiquitin-activating enzyme (E1), a ubiquitin-conjugating enzyme (E2), and a ubiquitin-protein ligase (E3) to catalyze ubiquitin chain formation on artificial substrates. E3 enzymes are thought to determine the substrate specificity of ubiquitination and have been classified into two families, the HECT and RING finger families. Six mammalian U box proteins have now been shown to mediate polyubiquitination in the presence of E1 and E2 and in the absence of E3. These U box proteins exhibited different specificities for E2 enzymes in this reaction. Deletion of the U box or mutation of conserved amino acids within it abolished ubiquitination activity. Some U box proteins catalyzed polyubiquitination by targeting lysine residues of ubiquitin other than lysine 48, which is utilized by HECT and RING finger E3 enzymes for polyubiquitination that serves as a signal for proteolysis by the 26 S proteasome. These data suggest that U box proteins constitute a third family of E3 enzymes and that E4 activity may reflect a specialized type of E3 activity.
authors: Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors: S
authors: S
authors: Hatakeyama
authors: M
authors: M
authors: Yada
authors: M
authors: M
authors: Matsumoto
authors: N
authors: N
authors: Ishida
authors: K I
authors: KI
authors: Nakayama
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D016384:Consensus Sequence; D017124:Conserved Sequence; D018076:DNA, Complementary; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008025:Ligases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008239:Lysine; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013737:Testis / Q000378:metabolism; D013950:Thymus Gland / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D005656:Fungal Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D044764:Ubiquitin-Activating Enzymes; C114683:UFD2 protein, S cerevisiae; D008239:Lysine