title: Bul1, a new protein that binds to the Rsp5 ubiquitin ligase in Saccharomyces cerevisiae.
abstract: We characterized a temperature-sensitive mutant of Saccharomyces cerevisiae in which a mini-chromosome was unstable at a high temperature and cloned a new gene which encodes a basic and hydrophilic protein (110 kDa). The disruption of this gene caused the same temperature-sensitive growth as the original mutation. By using the two-hybrid system, we further isolated RSP5 (reverses Spt- phenotype), which encodes a hect (homologous to E6-AP C terminus) domain, as a gene encoding a ubiquitin ligase. Thus, we named our gene BUL1 (for a protein that binds to the ubiquitin ligase). BUL1 seems to be involved in the ubiquitination pathway, since a high dose of UBI1, encoding a ubiquitin, partially suppressed the temperature sensitivity of the bul1 disruptant as well as that of a rsp5 mutant. Coexpression of RSP5 and BUL1 on a multicopy plasmid was toxic for mitotic growth of the wild-type cells. Pulse-chase experiments revealed that Bul1 in the wild-type cells remained stable, while the bands of Bul1 in the rsp5 cells were hardly detected. Since the steady-state levels of the protein were the same in the two strains as determined by immunoblotting analysis, Bul1 might be easily degraded during immunoprecipitation in the absence of intact Rsp5. Furthermore, both Bul1 and Rsp5 appeared to be associated with large complexes which were separated through a sucrose gradient centrifugation, and Rsp5 was coimmunoprecipitated with Bul1. We discuss the possibility that Bul1 functions together with Rsp5 in protein ubiquitination.
authors.affiliation: Department of Biological Sciences, Graduate School of Sciences, The University of Tokyo, Bunkyo-ku, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Yashiroda
authors.forename: T
authors.initials: T
authors.lastname: Oguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Yasuda
authors.forename: A
authors.initials: A
authors.lastname: Toh-E
authors.forename: Y
authors.initials: Y
authors.lastname: Kikuchi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004271:DNA, Fungal / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D016153:Genes, Suppressor; D005816:Genetic Complementation Test; D006801:Humans; D007700:Kinetics; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013012:Sorbitol / Q000378:metabolism; D013696:Temperature; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C099939:BUL1 protein, S cerevisiae; D002352:Carrier Proteins; D004271:DNA, Fungal; D056827:Endosomal Sorting Complexes Required for Transport; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D013012:Sorbitol; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; C469287:RSP5 protein, S cerevisiae