Coordinate effects of human immunodeficiency virus type 1 protein Tat and cellular protein Pur{{alpha}} on DNA replication initiated at the JC virus origin

Department of Pathology, Department of Molecular Biology and Biochemistry and the D. H. Ruttenberg Cancer Center, Box 1194, Mount Sinai School of Medicine, New York, NY 10029, USA 1 Center for Neurovirology and Cancer Biology, Temple University, Bio-Life Sciences Building, 1900 N. 12th Street, Philadelphia, PA 19122, USA 2 Author for correspondence: Edward M. Johnson. Fax +1 212 534 7491. e-mail edward.johnson{at}mssm.edu JC virus (JCV) causes progressive multifocal leukoencephalopathy, a demyelinating disease in brains of individuals with AIDS. Previous work has shown that the Tat protein, encoded by human immunodeficiency virus type 1 (HIV-1), can interact with cellular protein Pur to enhance both TAR-dependent HIV-1 transcription and JCV late gene transcription. Tat has been shown to activate JCV transcription through interaction with Pur , which binds to promoter sequence elements near the JCV origin of replication. DNA footprinting has shown that Pur and large T-antigen cooperatively interact at several binding sites in the origin and transcriptional control region. Overexpression of Pur inhibits replication initiated at the JCV origin by T-antigen. In transfected glial cells Tat reversed this inhibition and enhanced DNA replication. In an in vitro replication system maximal activation by Tat, more than sixfold the levels achieved with T-antigen alone, was achieved in the presence of Pur . Effects of mutant Tat proteins on both activation of replication and binding to Pur have revealed that Cys22 exerts a conformational effect that affects both activities. The origin of an archetypal strain of JCV was less susceptible to activation of replication by Tat relative to the rearranged Mad-1 strain. These results have revealed a previously undocumented role for Tat in DNA replication and have indicated a regulatory role for JCV origin auxiliary sequences in replication and activation by Tat.