Yeast surviving factor Svf1 as a new interacting partner, regulator and in vitro substrate of protein kinase CK2

Since Svf1 is phosphoprotein, we investigated whether it was a substrate for protein kinase CK2. According to the amino acid sequence Svf1 harbours 20 putative CK2 phosphorylation sites. Here, we have reported cloning, overexpression, purification and characterization of yeast Svf1 as a substrate for three forms of yeast CK2. Svf1 serves as a substrate for both the recombinant CK2 alpha (K (m) 0.35 mu M) and CK2 alpha' (K (m) 0.18 mu M) as well as CK2 holoenzyme (K (m) 1.1 mu M). Different K (m) values argue that CK2 beta(beta') subunit has an inhibitory effect on the activity of both CK2 alpha and CK2 alpha' towards surviving factor Svf1. Reconstitution of alpha'(2)beta beta' isoform of CK2 holoenzyme shows that beta/beta' subunits have regulatory effect depending on the kind of CK2 catalytic subunit. This effect was not observed in the case of alpha(2)beta beta' isoform, which may be due to interaction between Svf1 and regulatory CK2 beta subunit (shown by co-immunoprecipitation experiments). Interactions between CK2 subunits and Svf1 protein may have influence on ATP as well as ATP-competitive inhibitors (TBBt and TBBz) binding. CK2 phosphorylates up to six serine residues in highly acidic peptide K(199)EVIPESDEEESSADEDDNEDEDEESGDSEEESGSEEESDSEEVEITYED(248) of the Svf1 protein in vitro. Presented data may help to elucidate the role of protein kinase CK2 and Svf1 in the regulation of cell survival pathways.