FIG. 3.

CK2α is a shuttling protein. Stably transfected NIH 3T3 cells expressing either GFP-CK2α or GFP-CK2β were pretreated for 1 h with cycloheximide alone (A) or LMB and cycloheximide (B) and fused to nonexpressing HeLa cells. Cells were fixed 2 h after fusion and stained with Hoechst 33258 and with Texas Red-phalloidin to reveal cytoplasmic actin filaments, facilitating detection of heterokaryons with two or more nuclei. Mouse nuclei exhibit a speckled fluorescence when stained with Hoechst 33258 (arrows), while the human nuclei stain evenly, enabling the two to be distinguished easily. GFP fluorescence in the human nucleus is indicative of export of GFP-CK2α from the mouse nucleus (arrows). Each image is representative of >50 heterokaryons analyzed on each coverslip, and two independent heterokaryon assays were performed for each experimental condition. Bar, 5 μm.