Fig. 2. Putative reaction sequence of CSN/proteasome-mediated degradation of the tumour suppressor p53. CSN subunits modified by phosphorylation are indicated by red dots. Under normal growth conditions, p53 is continuously phosphorylated by the CSN-associated kinase. In the reaction scheme, unpublished data are included suggesting that the Ub ligase Mdm2 directly interacts with the CSN and presumably forms a temporary complex that contains p53 (S. Uhle and W. Dubiel, unpublished). Mdm2 might bind to the CSN-p53 complex after phosphorylation and ubiquitinate the tumour suppressor. At the moment, it is unclear how the p53-Ub conjugates are delivered to the 26S proteasome. The 19S regulator of the 26S proteasome consists of the LID and the BASE. In the figure, it is attached to only one side of the 20S proteasome, the proteolytic machinery.

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