To address the functional relevance of the ERj1 Olmesartan
by CK2, we tested whether the ERj1-ribosome interaction is regulated by this phosphorylation. It was previously observed for calnexin, another ER-resident membrane chaperone, that phosphorylation affects its interaction with the ribosome. A coordinated phosphorylation by CK2 and ERK-1 (extracellular signal regulated kinase-1) resulted in an enhanced association with the ribosome. In contrast, phosphorylation by CK2 alone led to dissociation from the ribosome . However, phosphorylation of ERj1 by protein kinase CK2 has no effect on the interaction between ERj1 and ribosomes (Fig. 4). Two scenarios can explain this observation; first, the ERj1-ribosome interaction is indeed not regulated by CK2 phosphorylation, and second, besides CK2 another kinase is required for the modulation of the ERj1-ribosome binding. Consistent with the latter idea, other phosphorylated ERj1 peptides
were identified that did not contain a canonical CK2 phosphorylation motif .