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Figure 5.
Figure 5. Model for coupled regulation of proteasome assembly
and inhibition. Proposed late steps in the assembly of the
proteasome are depicted. The inhibitory N-terminal sequences of
the  -subunits
and  -subunits
are represented in red. In the inactive half-CP, inhibition is
provided by the -subunit
propeptides (which directly block the proteolytic active sites).
Inhibition by the -subunit
tails becomes effective only when the half-CPs condense to form
a closed chamber. The inactive CP is converted to the latent
form upon autolysis of the -propeptides.
The last step represents holoenzyme formation, which is
accompanied by channel opening. For details, see the text. RP,
regulatory particle. The schematic representation of -propeptide-mediated
inhibition is modified from ref. 20.
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