Critical elements in proteasome assembly.
Coexpression of both subunits of the Thermoplasma proteasome in Escherichia coli yields fully assembled and proteolytically active proteasomes. Post-translational processing of the beta-subunit occurs in E. coli as it does in Thermoplasma. Coexpression of the alpha-subunit and the beta delta pro-subunit, a mutant beta-subunit lacking the propeptide, also yields fully assembled and active proteasomes. This indicates that the beta-propeptide is not essential for the folding and assembly of Thermoplasma proteasomes. Separately expressed alpha-subunits assemble into heptameric rings indistinguishable from the terminal rings of a proteasome. Mutational analysis shows that the amino terminus, which is highly conserved in all proteasomal alpha-type proteins, is essential for assembly. In the absence of alpha-subunits the beta-subunits are monomeric and post-translational processing of the beta-propeptide does not occur.
Zwickl
P
P
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Kleinz
J
J
Baumeister
W
W
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D009154:Mutation; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid; D013822:Thermoplasma / Q000201:enzymology*
D004792:Enzyme Precursors; D009097:Multienzyme Complexes; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex