Ectopically expressed IK proteins form nuclear foci during interphase, a process that requires its C-terminal region. A. HeLa cells were transfected with a plasmid expressing GFP or GFP-IK. Expression of GFP or GFP-IK was examined under a fluorescence microscope as described in Materials and methods. B. Schematic representation of the IK deletion constructs used in this experiment. C. IK deletion mutants were unable to form nuclear foci and present in both the nucleus and the cytoplasm during interphase. HeLa cells were transfected with indicated IK constructs and expressed proteins were examined under a fluorescence microscope as described in Materials and methods.