p13 is ubiquitinated in the presence of Tax. (A) 293T cells were transfected with p13 (4.0 μg; lanes 2 and 3) in the absence or presence of Tax (1.0 μg). Lysates were prepared with buffer containing NEM (10μM) and immunoblots were made with antibodies to Tax, HA, and tubulin. (B) 293T cells were transfected with Tax (1.0 μg) and Ub-WT (2.0 μg), Ub-K63 (2.0 μg), or Ub-K48 (2.0 μg) and p13-HA (4.0 μg) as indicated. Lysates were immunoblotted for the expression of Tax, p13-HA, and tubulin. Arrows indicate ubiquitinated forms of p13.