Specific binding of protein kinase CK2 catalytic subunits to tubulin

Protein kinase CK2 is composed of two regulatory β-subunits and two catalytic α- or α′-subunits. To analyse these subunits individually we generated antibodies against unique peptides derived from the α-, α′- and β-subunit. Immunofluorescence studies with these antibodies revealed the presence of all three CK2 subunits in the cytoplasm and weakly in the nucleus with strong signals around the nuclear membrane. Double staining experiments revealed a co-localisation of all three subunits with tubulin. A direct association between the CK2 α- and the α′-subunit and tubulin was confirmed by co-immunoprecipitation experiments as well as by Far Western analysis. There was no binding of the CK2 β-subunit to tubulin. Thus, with tubulin we have identified a new binding partner specific for the catalytic subunits of CK2.