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C termini of proteasomal ATPases play nonequivalent roles in cellular assembly of mammalian 26 S proteasome.

The 26 S proteasome comprises two multisubunit subcomplexes as follows: 20 S proteasome and PA700/19 S regulatory particle. The cellular mechanisms by which these subcomplexes assemble into 26 S proteasome and the molecular determinants that govern the assembly process are poorly defined. Here, we demonstrate the nonequivalent roles of the C termini of six AAA subunits (Rpt1-Rpt6) of PA700 in 26 S proteasome assembly in mammalian cells. The C-terminal HbYX motif (where Hb is a hydrophobic residue, Y is tyrosine, and X is any amino acid) of each of two subunits, Rpt3 and Rpt5, but not that of a third subunit Rpt2, was essential for assembly of 26 S proteasome. The C termini of none of the three non-HbYX motif Rpt subunits were essential for cellular 26 S proteasome assembly, although deletion of the last three residues of Rpt6 destabilized the 20 S-PA700 interaction. Rpt subunits defective for assembly into 26 S proteasome due to C-terminal truncations were incorporated into intact PA700. Moreover, intact PA700 accumulated as an isolated subcomplex when cellular 20 S proteasome content was reduced by RNAi. These results indicate that 20 S proteasome is not an obligatory template for assembly of PA700. Collectively, these results identify specific structural elements of two Rpt subunits required for 26 S proteasome assembly, demonstrate that PA700 can be assembled independently of the 20 S proteasome, and suggest that intact PA700 is a direct intermediate in the cellular pathway of 26 S proteasome assembly.

Pubmed ID: 21628461


  • Kim YC
  • DeMartino GN


The Journal of biological chemistry

Publication Data

July 29, 2011

Associated Grants

  • Agency: NIDDK NIH HHS, Id: R01 DK046181
  • Agency: NIDDK NIH HHS, Id: R01 DK46181

Mesh Terms

  • Adenosine Triphosphatases
  • Amino Acid Motifs
  • Amino Acid Sequence
  • HEK293 Cells
  • Humans
  • Proteasome Endopeptidase Complex
  • Protein Structure, Tertiary
  • Sequence Deletion