Yashiroda H, Toda Y, Otsu S, Takagi K, Mizushima T, Murata S

The proteasome core particle (CP) is a conserved protease complex that is formed by the stacking of two outer α-rings and two inner β-rings. The α-ring is a heteroheptameric ring of α1-α7 subunits and acts as a gate that restricts entry of substrate proteins into the catalytic cavity formed by ...

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the two abutting β-rings. Proteasome inhibitor 31-kDa (PI31) was originally identified as a protein that binds to the CP and inhibits CP activity in vitro, but accumulating evidence indicates that PI31 is required for physiological proteasome activity. To clarify the in vivo role of PI31, we examined the yeast Saccharomyces cerevisiae PI31 ortholog, Fub1. Fub1 was essential in a situation where the CP assembly chaperone Pba4 was deleted. The lethality of Δfub1Δpba4 was suppressed by deletion of the N-terminus of α7 (α7ΔN), which leads to the partial activation of the CP. However, deletion of the N-terminus of α3, which activates the CP more efficiently than α7ΔN by gate opening, did not suppress the Δfub1Δpba4 lethality. These results suggest that the α7 N-terminus has a different role in CP activation from the α3 N-terminus and that the role of Fub1 antagonizes a specific function of the α7 N-terminus.

Date: Oct. 20, 2014

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