Tacaribe virus Z protein interacts with the L polymerase protein to inhibit viral RNA synthesis.

Tacaribe virus (TV) is the prototype of the New World group of arenaviruses. The TV genome encodes four proteins, the nucleoprotein (N), the glycoprotein precursor, the polymerase (L), and a small RING finger protein (Z). Using a reverse genetic system, we recently demonstrated that TV N and L are sufficient to drive transcription and full-cycle RNA replication mediated by TV-like RNAs and that Z is a powerful inhibitor of these processes (N. López, R. Jácamo, and M. T. Franze-Fernández, J. Virol. 65:12241-12251, 2001). In the present study we investigated whether Z might interact with either of the proteins, N and L, required for RNA synthesis. To that end, we used coimmunoprecipitation with monospecific antibodies against the viral proteins and coimmunoprecipitation with serum against glutathione S-transferase (GST) and binding to glutathione-Sepharose beads when Z was expressed as a fusion protein with GST. We demonstrated that Z interacted with L but not with N and that Z inhibitory activity was dependent on its ability to bind to L. We also evaluated the contribution of different Z regions to its binding ability and functional activity. We found that integrity of the RING structure is essential for Z binding to L and for Z inhibitory activity. Mutants with deletions at the N and C termini of Z showed that amino acids within the C-terminal region and immediately adjacent to the RING domain N terminus contribute to efficient Z-L interaction and are required for inhibitory activity. The data presented here provide the first evidence of an interaction between Z and L, suggesting that Z interferes with viral RNA synthesis by direct interaction with L. In addition, coimmunoprecipitation studies revealed a previously unreported interaction between N and L.