The axial channel of the proteasome core particle is gated by the Rpt2 ATPase and controls both substrate entry and product release

Substrates enter the proteasome core particle (CP) through a channel that o pens upon association with the regulatory particle (RP). Using yeast mutant s, we show that channel opening is mediated by the ATPase domain of Rpt2, o ne of six ATPases in the RP. To test whether degradation products exit thro ugh this channel, we analyzed their size distribution. Their median length from an open-channel CP mutant was 40% greater than that from the wild-type . Thus, channel opening may enhance the yield of peptides long enough to fu nction in antigen presentation. These experiments demonstrate that gating o f the RP channel controls both substrate entry and product release, and is specifically regulated by an ATPase in the base of the RP.