IK is a stable protein required for cell cycle progression. A. HeLa cells were transfected with either control siRNA (targeting luciferase) or IK siRNA. Forty eight hours after transfection, cells were photographed under a phase-contrast microscope. B. HeLa cells were transfected with IK siRNA. IK protein levels were followed at indicated time points by Western blot with an anti-IK antibody. C. HeLa cells were transfected as in A and DNA content of the cells were analyzed by flow cytometry 48 hours after transfection. D. Half-life analysis of IK protein was determined after treatment with cycloheximide (CHX) followed by Western blot with the anti-IK antibody.