DNA binding of TopoIIα increases susceptibility of SUMOylation at Lys660. (a) TopoIIα WT in vitro SUMOylation reactions were performed with or without DNA. The samples were analyzed with anti-T7 tag antibody Western blots. The presence of DNA in the SUMOylation reactions significantly stimulates TopoIIα WT SUMOylation. (b) TopoIIα WT and TopoIIα K660R were subjected to in vitro reactions under the same condition as in a except for using 5 ng/µl of DNA. PARP1, a mitotic chromosomal SUMO2/3 substrate, was used as a control. A deficiency of TopoIIα K660R SUMOylation was observed in the presence of DNA compared with TopoIIα WT. Positions of molecular mass standards (kD) are indicated on the left.