In Vivoandin VitroPhosphorylation of the α7/PRS1 Subunit ofSaccharomyces cerevisiae20 S Proteasome:In VitroPhosphorylation by Protein Kinase CK2 Is Absolutely Dependent on Polylysine

In this paper, we show that theSaccharomyces cerevisiae20 S proteasome subunit 1 (PRS1), recently renamed as α7, is the mainin vivophosphorylated andin vitroCK2-phosphorylatable proteasome component.In vitrophosphorylation occurs only in the presence of polylysine, a characteristic that distinguishes the yeast proteasome from mammalian ones which are phosphorylated by CK2 in the absence of polylysine. A peptide reproducing the long acidic C-terminal tail of α7/PRS1, where consensus CK2 phosphorylation sites are located, was also phosphorylated by the CK2 holoenzyme in a polylysine-dependent manner, suggesting that this region contains structural features responsible for this particular behavior.