Topoisomerase activity associated with polyoma virus large tumor antigen

摘要

Polyomavirus (Py) large tumor antigen (LT) was produced in mammalian or insect cells infected with a suitable viral expression vector, iiiul purified by a procedure combining immunoprecipitation with ion-exchange chromatography. Fractions containing the bulk of LT displayed :> DNA-rclaxtng activity (LT-topo) which could be attributed neither to topoisomerase II (topo II) nor to topoisomerase I (top*i 1) encoded by the cell or the viral vector. On the one hand, LT-topo relaxed pBR322 DNA in a reaction which, unlike that characteristic of lopo II, was ATP-independent and inhibited by camptothecin. On the other hand, serum from scleroderma patients which strongly inhibited call' thymtis topo I hud no effect on LT-topo, which absolutely required Mg2+ ions to relax DNA. Thus, LT-topo is either iiilicrciil to LT or belongs to a LT-bound enzyme similar to, but distinct from, topo I.