Visualization and molecular analysis of nuclear import of protein kinase CK2 subunits in living cells

We have generated fusion proteins between the subunits of CK2 and GFP and c haracterized their behaviour in living cells. The expressed fusion proteins were functional and interacted with endogenous CK2. Imaging of NIH3T3 cell s expressing low level of GFP-CK2 alpha or GFP-CK2 beta showed that both pr oteins were mostly nuclear in interphase. Both CK2 subunits contain nuclear localization domains that target them independently to the nucleus. Once i n the nucleus, both subunits diffused rapidly in the nucleoplasm. In mitoti c cells, CK2 subunits were dispersed throughout the cytoplasm and were not associated to chromatin. Our data are compatible with the idea that each su bunit can translocate individually to the nucleus to interact with each oth er or with important cellular partners. Understanding the molecular mechani sms which regulate the dynamic localization of CK2 subunits will be of cent ral importance.