N-terminal ?7 deletion of the proteasome 20S core particle substitutes for yeast PI31 function.

ABSTRACT: The proteasome core particle (CP) is a conserved protease complex that is formed by the stacking of two outer ?-rings and two inner ?-rings. The ?-ring is a heteroheptameric ring of subunits ?1 to ?7 and acts as a gate that restricts entry of substrate proteins into the catalytic cavity formed by the two abutting ?-rings. The 31-kDa proteasome inhibitor (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 Saccharomyces cerevisiae PI31 ortholog Fub1. Fub1 was essential in a situation where the CP assembly chaperone Pba4 was deleted. The lethality of ?fub1 ?pba4 was suppressed by deletion of the N terminus of ?7 (?7?N), which led to the partial activation of the CP. However, deletion of the N terminus of ?3, which activates the CP more efficiently than ?7?N by gate opening, did not suppress ?fub1 ?pba4 lethality. These results suggest that the ?7 N terminus has a role in CP activation different from that of the ?3 N terminus and that the role of Fub1 antagonizes a specific function of the ?7 N terminus.

SUBMITTER: Yashiroda H 

PROVIDER: S-EPMC4295373 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature