Abstract
The proteasome is the central regulatory protease of eukaryotic cells. Heteroheptameric α-subunit and β-subunit rings stack to form the 20S proteasome, which associates with a 19S regulatory particle (RP). Here we show that two yeast proteins, Pba3 and Pba4, form a previously unidentified 20S proteasome–assembly chaperone. Pba3–Pba4 interacts genetically and physically with specific proteasomal α subunits, and loss of Pba3–Pba4 causes both a reduction and a remodeling of cellular proteasomes. Notably, mutant cells accumulate proteasomes in which a second copy of the α4 subunit replaces α3. 20S proteasome–assembly defects also are associated with altered RP assembly; this unexpected result suggests that the 20S proteasome can function as an RP-assembly factor in vivo. Our data demonstrate that Pba3–Pba4 orchestrates formation of a specific type of proteasome, the first example of a trans-acting factor that controls assembly of alternative proteasomal complexes.
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Acknowledgements
We thank D. Finley (Harvard University, Boston) and W. Heinemeyer (University of Stuttgart, Germany) for antibodies to proteasome subunits. This work was supported by grants from the US National Institutes of Health (NIH) to M.H. A.R.K. was supported in part by a postdoctoral fellowship from the Canadian Institutes of Health Research. M.J.K. was supported by NIH training grant GM007223.
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A.R.K. and M.H. developed the experimental approach. A.R.K., M.J.K., M.F. and M.H. carried out experiments. A.R.K. and M.H. wrote the paper.
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Kusmierczyk, A., Kunjappu, M., Funakoshi, M. et al. A multimeric assembly factor controls the formation of alternative 20S proteasomes. Nat Struct Mol Biol 15, 237–244 (2008). https://doi.org/10.1038/nsmb.1389
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DOI: https://doi.org/10.1038/nsmb.1389
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