SUMO modification affects the decatenation activity of TopoIIα. (a) T7-TopoIIα was incubated with various combinations of Ubc9/PIASy as indicated to obtain a series of SUMOylation profiles. All control reactions (Cont.) were performed with 60 nM Ubc9/10 nM PIASy and SUMO2-G, which could not be conjugated. The samples were analyzed by Western blotting for the T7 tag. The arrow indicates maximal SUMO modification of TopoIIα (seen in 30/30 and 60/10). Positions of molecular mass standards (kD) are indicated on the right. (b) Representative data of decatenation assay. Samples in a were further incubated with decatenation buffer that contained kDNA for 10 or 20 min, and the products were resolved in an agarose gel. Decatenated and linearized markers are designated. (c) Band intensity data from five independent experiments performed as in b are presented as the percentage of catenated kDNA remaining after a 20-min incubation, with standard error (error bars) and probability value from a Student’s t test. SUMO2 modification of TopoIIα decreased its decatenation activity.