Ubiquitin-independent Proteolysis

The 26S proteasome also degrades non-ubiquitylated proteins [71]. The short-lived enzyme ornithine decarboxylase (ODC) and the cell-cycle regulator p21Cip provide well documented examples of ubiquitin-independent proteolysis by the 26S en-... 

After the discovery of this multicatalytic proteinase complex, which has a sedimentation coefficient of 20 S, it was realised that it was very similar to another particle that had been isolated independently. The latter, known as a prosome, is associated with mRNA that is repressed from translation. Generally a cell has two pools of mRNA, one that is being actively translated and the other that is inhibited from translation. Prosome-like particles have been detected in duck erythroblasts where they inhibit translation of the portion of the mRNA that is bound to the erythroblasts (Akhayat et al, 1967 Nothwang et al, 1992). The multicatalytic proteinase (20S) associates with two factors (CFl and CF2) to form a 26S complex referred to as a proteasome (Fig. 5.4). The proteasome (26S) and the multicatalytic proteinase complex (20S) are thought to participate in ubiquitin-dependent and ubiquitin-independent proteolysis, respectively. 

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