In vivo and in vitro phosphorylation of the α7/PRS1 subunit of Saccharomyces cerevisiae 20 S proteasome: In vitro phosphorylation by protein kinase CK2 is absolutely dependent on polylysine

In this paper, we show that the Saccharomyces cerevisiae 20 S proteasome subunit 1 (PRS1), recently renamed as α7, is the main in vivo phosphorylated and in vitro CK2-phosphorylatable proteasome component. In vitro phosphorylation 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.