A DNA‐Topoisomerase‐11–Binding Protein with Eight Repeating Regions Similar to DNA‐repair Enzymes and to a Cell‐Cycle Regulator

Abstract

A two‐hybrid system was used to isolate factors that interact with the C‐terminal region of DNA topoisomerase IIβ. A positive clone isolated from a HeLa cDNA library encoded 1.522 amino acid residues (molecular mass 170670). The protein, designated topoisomerase‐IIβ‐binding protein 1 (TopBP1), interacted with the C‐terminal region of topoisomerase IIβ synthesized in vitro. A database search indicated that TopBP1 possessed eight regions similar to regions of Rad4, Cut.5, Ect2, Revl and X‐ray repair cross‐complementing 1 (XRCC1) proteins and a region similar to auto‐modification sites of poly(ADP ribose) polymerase, suggesting that TopBP1 supported catalytic reactions of opoisomerase II through transient breakages of DNA strands.