Identification of proteins that associate with protein kinase CK2

In order to aid in an understanding of the cellular functions of protein ki nase CK2, a search for interacting proteins was carried out using a P-32-la beled 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 e xperiments involving the co-immunoprecipitation using anti-CK2 antibodies. Further analysis using GST-CK2 fusion proteins demonstrated that the CK2-p1 10 interaction occurred through the CK2 alpha/alpha' subunits. To identify p110, it was purified using a GST-CK2 affinity column, and internal amino a cid sequencing was then performed. p110 was found to be nucleolin, a nucleo lar protein that may be important for rRNA synthesis; a possible role of CK 2 in the control of this process is suggested. Using the same CK2 overlay t echnique, another interacting protein, insulin receptor substrate 1 (IRS-1) , was also identified. By applying a modified overlay method using individu al S-35-labeled CK2 subunits, obtained by in vitro translation in rabbit re ticulate 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 kn own substrate for CK2. However, further work is needed to examine the assoc iation of CK2 with IRS-I in vivo in order to fully understand the significa nce of the interaction.