Phosphorylation of proteasome and 26S proteinase subunits

The multicatalytic proteinase complex, the proteasome, is found in cells to be associated with other multimeric proteins giving. rise to a number of very large complexes. The proteasome, probably as part of these larger complexes, plays an important role in the non-lysosomal degradation of intracellular proteins, in antigen processing and in cellular regulation through the degradation of short-lived regulatory proteins. One such complex is the 26S proteinase which consists of a core proteasome with 19S regulatory complexes bound at both ends. Under mild conditions the proteasome can be purified in an inactive form and in vivo it is presumably via interactions with the various regulatory proteins of the larger complexes that the activity of the proteasome is activated and regulated. The roles played by these complexes suggest that their activities must be closely regulated. The mechanisms of such regulation is not known but there is some evidence that, as with many other important cellular events, phosphorylation may play a part. This article focuses on our studies to determine whether any subunits of the proteasome and 26S proteinase are phosphorylated and what regulatory roles these modifications may play.