Tax-P79AQ81A is defective for SUMOylation. NiNTA experiments performed in HeLa cells showing the total level of Tax modifications (A), or the amounts of Tax products conjugated to endogenous total ubiquitin (B), endogenous K63-linked ubiquitin chains (C), endogenous SUMO (D) or overexpressed HA-SUMO-1 (E) for either wt Tax and Tax-P79AQ81A. (A-D) HeLa cells were transfected with a control plasmid or each of the Tax-His constructs and in (E) along with a HA-SUMO-1 construct. Tax proteins purified using nickel columns were revealed with anti-Tax sera or with anti-Ubiquitin, anti-K63-linked ubiquitin chains, anti-SUMO-2/3 or anti-HA antibodies, as indicated. The percentage of Tax modification was calculated by dividing the amount of high molecular weight Tax products by the amount of total Tax (modified + unconjugated). The percentages of ubiquitinated or SUMOylated Tax were normalized on the amount of unconjugated Tax (Tax-Ub/Tax) and expressed in comparison to wt Tax (100%).