Facilitation of proteasomal degradation of p27 Kip1 by N-terminal cleavage and their sequence requirements

Abstract

The sequence requirement for N-terminal cleavage and the proteasomal degradation of p27 Kip1 and their relationship was investigated. Residues 5–8 were required for the cleavage and the mutation of S10 to E inhibited the cleavage. The C-terminal PEST sequence was necessary for the degradation and residue R165 was found to play an important role in the degradation. The inhibition of the cleavage by deleting residues 5–8 inhibited the degradation, while the fragment mimicking the cleavage product accelerated the degradation. Both the cleavage and degradation demonstrated a similar sensitivity toward proteasome inhibitors and ATP depletion. These two processes are thus suggested to be tightly linked and sequential.