Identification of proteins that associate with protein kinase CK2

In order to aid in an understanding of the cellular functions of protein kinase CK2, a search for interacting proteins was carried out using a P-32-labeled CK2 overlay method. Several proteins were found to associate with CK2 by this assay, among them, one protein of 110 kDa appeared to be the most prominent one. The possible association of CK2 with p110 was suggested by experiments involving the co-immunoprecipitation using anti-CK2 antibodies. Further analysis using GST-CK2 fusion proteins demonstrated that the CK2-p110 interaction occurred through the CK2 alpha/alpha' subunits. To identify p110, it was purified using a GST-CK2 affinity column, and internal amino acid sequencing was then performed. p110 was found to be nucleolin, a nucleolar protein that may be important for rRNA synthesis; a possible role of CK2 in the control of this process is suggested. Using the same CK2 overlay technique, another interacting protein, insulin receptor substrate 1 (IRS-1), was also identified. By applying a modified overlay method using individual S-35-labeled CK2 subunits, obtained by in vitro translation in rabbit reticulate lysates, it was determined that CK2 associates with IRS-I through its alpha/alpha' subunits; i.e. in keeping with the fact that IRS-1 is a known substrate for CK2. However, further work is needed to examine the association of CK2 with IRS-I in vivo in order to fully understand the significance of the interaction.