Nob1p is required for biogenesis of the 26S proteasome and degraded upon its maturation in Saccharomyces cerevisiae.
Nob1p is a nuclear protein that forms a complex with the 19S regulatory particle of the 26S proteasome and with uncharacterized nuclear protein Pno1p. Overexpression of NOB1 overrode the defects in maturation of the 20S proteasome of ump1Delta cells, and temperature-sensitive nob1 and pno1 mutants exhibited defects in the processing of the beta subunits and in the assembly of the 20S and the 26S proteasomes. A defect in either NOB1 or PNO1 caused accumulation of newly formed Pre6p in the cytoplasm, whereas Pre6p of the ump1Delta strain accumulated in the nucleus irrespective of the temperature. Here we present a model proposing that (1) Nob1p serves as a chaperone to join the 20S proteasome with the 19S regulatory particle in the nucleus and facilitates the maturation of the 20S proteasome and degradation of Ump1p, and (2) Nob1p is then internalized into the 26S proteasome and degraded to complete 26S proteasome biogenesis.
Tone
Yoshiko
Y
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Japan.
Toh-E
Akio
A
D000251:Adenosine Triphosphatases; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000502:physiology*; D017931:DNA Primers / Q000737:chemistry; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D015966:Gene Expression Regulation, Fungal; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D010447:Peptide Hydrolases / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D014452:Ubiquitins / Q000378:metabolism
D002352:Carrier Proteins; D017931:DNA Primers; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D018832:Molecular Chaperones; C405962:NOB1 protein, S cerevisiae; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; C110856:proteasome maturation protein; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D000251:Adenosine Triphosphatases; C084493:RPT1 protein, S cerevisiae