Exogenous p19Arf detected by immunofluorescence. Cells were transduced and, 24 hours later, fixed with methanol and exposed to a polyclonal antibody for p19Arf and a monoclonal antibody for p53 and detection with Alexa-488 anti-rabbit and Cy3 anti-mouse secondary antibodies. Cells were then stained with Hoechst 33258. For B16, we show only the 20 × magnification confocal photomicrographs, no staining of p53 was visible at higher magnification. For C6, the appearance of p19Arf at 20 × magnification was comparable to that shown for B16, however endogenous p53 staining was observed in C6. We show C6 at 20 × magnification plus 4 × zoom in order to emphasize p53 staining. All photos for either B16 or C6 were captured using identical settings. Merge refers to the combined images of the green, red and blue channels.