Pak3 augments Tax-induced HTLV-1 LTR activation in a kinase-independent manner. (A) Expression of wild-type and mutant forms of Pak3. HeLa cells were transfected with expression plasmids for the indicated Pak3 proteins. Cells were harvested 48 hrs post transfection. The harvested cells were untreated or treated with calf intestinal phosphatase (CIP) at 37°C for 30 min. Proteins were analyzed by Western blotting with anti-myc and anti-α-tubulin antibodies, respectively. (B) Activity profile of Pak3 wild-type and mutants on Tax-induced LTR activation. Dual luciferase assays were carried out as in Figure 1.