Phospholipid Modulates In Vitro Replication of Autonomous Replicating Sequence from Human Cells¹

A cloned plasmid, pmyc(H-K), containing sequences derived from human c-myc gene replicated in vitro in Raji nuclear extract in a semiconservative manner. Using this system, it was found that phosphatidylinositol and cardiolipin strongly inhibited the replication of pmyc(H-K) in vitro, whereas other phospholipids, i.e., phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid, and sphingomyelin, had no appreciable effect. The concentrations of phosphatidylinositol and cardiolipin producing 50% inhibition of the replication were 4.6 and 5.4 µM, respectively. Phosphatidylinositol and cardiolipin inhibited the relaxation of pmyc(H-K) supercoiled DNA, but showed little or weaker effects on DNA polymerase α and topoisomerase II in Raji nuclear extract. These results suggest that phosphatidylinositol and cardiolipin antagonize the replication of pmyc(H-K) in vitro, through, at least in part, the interaction with topoisomerase I.