Figure 1

Network diagram of the ubiquitin-proteasome model. (a) Reactions leading to the first ubiquitination step; (b) reactions of chain lengthening and shortening (only shown for chains up to length four); (c) binding of substrate with polyubiquitin chains (of length four or more) to proteasome and chain shortening of bound substrates by DUBs which leads to release from proteasome when chain is less than four; (d) degradation of substrates by proteasome in ATP-dependent manner releasing ubiquitin for recycling; (e) formation of aggregated proteins, sequestering of aggregates and proteasome inhibition by aggregates.