title: The alpha4 and alpha7 subunits and assembly of the 20S proteasome.
abstract: The detailed mechanism of eukaryotic 20S proteasome assembly is currently unknown. In the present study, we demonstrate that the 20S proteasome subunits alpha4 and alpha7 interact with each other as well as all the alpha-subunits in vivo and in vitro. The N-terminal parts of alpha4 and alpha7 are essential for these newly discovered interactions in vitro. Glycerol gradient centrifugation of soluble extracts of HEK293 cells and Western blot analyses show that several alpha-subunits are found in non-proteasomal low-density fractions. The alpha4 and alpha7 subunits co-immunoprecipitate together from these low-density fractions. The unexpected interaction between alpha4 and alpha7 may provide a molecular basis for the formation of previously reported 13S and 16S assembly intermediates.
authors.affiliation: Laboratory of Intracellular Proteolysis, School of Biomedical Sciences, University of Nottingham, Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK.
authors.forename: Géraud-Sébastien
authors.initials: GS
authors.lastname: Apcher
authors.forename: Joanne
authors.initials: J
authors.lastname: Maitland
authors.forename: Simon
authors.initials: S
authors.lastname: Dawson
authors.forename: Paul
authors.initials: P
authors.lastname: Sheppard
authors.forename: R John
authors.initials: RJ
authors.lastname: Mayer
mesh_terms: D001665:Binding Sites; D002458:Cell Fractionation; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D005822:Genetic Vectors; D006801:Humans; D009097:Multienzyme Complexes / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016296:Mutagenesis; D046988:Proteasome Endopeptidase Complex; D021122:Protein Subunits / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D014461:Ultracentrifugation
chemical_list: D009097:Multienzyme Complexes; D021122:Protein Subunits; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases; C488662:PSMA7 protein, human; D046988:Proteasome Endopeptidase Complex; C488661:alpha4 subunit, proteasome 20S, human