EFFICIENT RETROVIRAL INFECTION OF MAMMALIAN-CELLS IS BLOCKED BY INHIBITION OF POLY(ADP-RIBOSE) POLYMERASE-ACTIVITY

Integration of proviral DNA into the host cell genome is a characteris tic feature of the retroviral life cycle. This process involves coordi nate DNA strand break formation and rejoining reactions. The full deta ils of the integration process are not yet fully understood. However, the endonuclease and DNA strand-joining activities of the virus-encode d integrase protein (IN) are thought to act ih concert with other, as- yet-unidentified, endogenous nuclear components which are involved in the DNA repair process. The nuclear enzyme poly(ADP-ribose) polymerase (PARP), which is dependent on DNA strand breaks for its activity, is involved in the efficient repair of DIVA strand breaks, and maintenanc e of genomic integrity, in nucleated eukaryotic cells, In the present work, we examine the possible involvement of PARP in the retroviral li fe cycle and demonstrate that inhibition of PARP activity, by any one of three independent mechanisms, blocks the infection of mammalian cel ls by recombinant retroviral vectors, This requirement for PARP activi ty appears to be restricted to processes involved in the integration o f provirus into the host cell DNA. PARP inhibition does not affect vir al entry into the host cell, reverse transcription of the viral RNA ge nome, postintegration synthesis of viral gene products, synthesis of t he viral RNA genome, or the generation of infective virions. Therefore , efficient retroviral infection of mammalian cells is blocked by inhi bition of PARP activity.