Hexameric assembly of the proteasomal ATPases is templated through their C termini.
Substrates of the proteasome are recognized and unfolded by the regulatory particle, and then translocated into the core particle (CP) to be degraded. A hetero-hexameric ATPase ring, containing subunits Rpt1-6, is situated within the base subassembly of the regulatory particle. The ATPase ring sits atop the CP, with the Rpt carboxy termini inserted into pockets in the CP. Here we identify a previously unknown function of the Rpt proteins in proteasome biogenesis through deleting the C-terminal residue from each Rpt in the yeast Saccharomyces cerevisiae. Our results indicate that assembly of the hexameric ATPase ring is templated on the CP. We have also identified an apparent intermediate in base assembly, BP1, which contains Rpn1, three Rpts and Hsm3, a chaperone for base assembly. The Rpt proteins with the strongest assembly phenotypes, Rpt4 and Rpt6, were absent from BP1. We propose that Rpt4 and Rpt6 form a nucleating complex to initiate base assembly, and that this complex is subsequently joined by BP1 to complete the Rpt ring. Our studies show that assembly of the proteasome base is a rapid yet highly orchestrated process.
Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
Soyeon
S
Park
Jeroen
J
Roelofs
Woong
W
Kim
Jessica
J
Robert
Marion
M
Schmidt
Steven P
SP
Gygi
Daniel
D
Finley
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
C112193:HSM3 protein, S cerevisiae; D018832:Molecular Chaperones; C114551:NAS6 protein, S cerevisiae; C499663:RPN1 protein, S cerevisiae; C521692:Rpt3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C103015:RPT4 protein, S cerevisiae; C541345:RPT5 protein, S cerevisiae; C069670:RPT6 protein, S cerevisiae