Gammaherpesviruses subvert eukaryotic signaling pathways to favor latent infections in their cellular reservoirs. To this end, they express proteins that regulate or replace functionally specific signaling proteins of eukaryotic cells. Here we describe a new type of such viral-host interaction that is established through M2, a protein encoded by murine gammaherpesvirus 68. M2 associates with Vav proteins, a family of phosphorylation-dependent Rho/Rac exchange factors that play critical roles in lymphocyte signaling. M2 expression leads to Vav1 hyperphosphorylation and to the subsequent stimulation of its exchange activity towards Rac1, a process mediated by the formation of a trimolecular complex with Src kinases. This heteromolecular complex is coordinated by proline-rich and Src family-dependent phosphorylated regions of M2. Infection of Vav-deficient mice with gammaherpesvirus 68 results in increased long-term levels of latency in germinal center B lymphocytes, corroborating the importance of the M2/Vav cross talk in the process of viral latency. These results reveal a novel strategy used by the murine gammaherpesvirus family to subvert the lymphocyte signaling machinery to its own benefit.This work was supported by grants to J.P.S. from the Portuguese Fundaçao para a Ciência e Tecnologia (POCTI/ESP/34240/2000) and to X.R.B. from both the U.S. National Cancer Institute (5RO1- CA073735-09) and the Spanish Ministry of Education and Science (MES) Biomedicine Program (SAF2003-00028). L.R. and M.M. were recipients of fellowships from the Fundaçao para a Ciência e Tecnologia. M.J.C. is a researcher of the MES Ramón y Cajal Program.Peer reviewed