HOMOLOGOUS AND HETEROLOGOUS PROTEIN-PROTEIN INTERACTIONS OF HUMAN DNATOPOISOMERASE II-ALPHA

DNA topoisomerase II (topo II; EC 5.99.1.3) is a nuclear enzyme whose DNA decatenating activity on newly replicated DNA is essential to succ essful cell division. Topo II catalytic activity proceeds by a concert ed DNA breakage-reunion reaction coordinated between two interacting, homologous subunits. Human and yeast topo II have recently been shown to enter into heterologous protein-protein interactions and some of th ese interactions appear necessary for successful chromosomal segregati on, In the present study, the sequences mediating homologous and heter ologous protein-protein interactions have been investigated biochemica lly using various truncated peptides from the major CY form of human t opo II. From nonreducing gel electrophoresis and solid-phase protein-p rotein binding (Far Western) assays, topo II homodimerization appeared to be minimally governed by the region between amino acids 951 and 10 42. However, maximal homodimerization and multimerization required seq uences C-terminal to position 1042. Topo II peptides were also able to interact with 10-12 nuclear proteins from HeLa cells, termed topo II- interactive proteins or TIPs, Interestingly, small topo II peptides be tween residues 808 and 951 that did not homodimerize with topo II (857 -1447) were nonetheless capable of binding to HeLa TIPs, These interac tions were confirmed by use of topo II affinity chromatography for iso lation of specific TIPs from HeLa nuclear extracts, Taken together, th ese data confirm that human topo II is also capable of heterologous in teractions with nuclear proteins and that the region governing these i nteractions is distinct from, but has some overlap with, sequences dir ecting topo II homodimerization, (C) 1997 Academic Press.