Figure 7.

SLBP does not contain nuclear export signals. U2-OS cells were transfected with plasmids expressing GFP-SLBP wt (A) or the RNA binding mutant GFP-SLBP mut (B), which contains two tyrosines in the RBD replaced with alanines (Dominski et al., 2001). Twenty-four hours after transfection, the cells were washed and fused to wild-type MEF cells, and de novo protein synthesis was blocked by cycloheximide. Ninety minutes after fusion, the cells were fixed and stained with an antibody to human Ku antigen followed by staining with a Texas Red-conjugated secondary antibody. The heterokaryons were photographed. Nuclei of human (h) and mouse (m) origin are identified by DAPI staining. Mouse nuclei are indicated with white arrows.