Phosphorylation by Casein Kinase 2 Facilitates Psh1 Assisted Degradation of Cse4 [Protein Synthesis and Degradation]

September 2nd, 2014 by Hewawasam, G. S., Mattingly, M., Venkatesh, S., Zhang, Y., Florens, L., Workman, J. L., Gerton, J. L.

Cse4 is the centromeric histone H3 variant (CenH3) in budding yeast. Psh1 is an E3 ubiquitin ligase which controls Cse4 levels through proteolysis. Here we report Psh1 is phosphorylated by the Cka2 subunit of Casein Kinase 2 (CK2) to promote its E3 activity for Cse4. Deletion of CKA2, similar to psh1Δ, significantly stabilized Cse4. Consistent with phosphorylation promoting the activity of Psh1, Cse4 is stabilized in a Psh1 phospho-deplete mutant strain in which the major phosphorylation sites are changed to alanines. Phosphorylation of Psh1does not control Psh1/Cse4 or Psh1/Ubc3(E2) interactions. Even though Cse4 is highly stabilized in a cka2Δ strain, mislocalization of Cse4 is mild, suggesting Cse4 misincorporation is prevented by the intact Psh1/Cse4 association. Supporting this idea, Psh1 is also stabilized in a cka2Δ strain. Collectively our data suggest phosphorylation is crucial in Psh1-assisted control of Cse4 levels and the Psh1/Cse4 association itself functions to prevent Cse4 misincorporation.