Mammalian inositol-specific phospholipase Cβ1 (PLCβ1) is activated by Gαq subunits on the plasma membrane where it catalyzes hydrolysis of the minor membrane phosphatidylinositol 4,5 bisphosphate. While PLCβ1 localizes primarily to the plasma membrane it also exists in other compartments of the cell. It is not currently known what function PLCβ1 has in the cytosol and nucleus nor is it known what factors localize PLCβ1 to these compartments. In this study, we have identified a novel binding partner, translin-associated factor X (TRAX). Our experiments show that both proteins interact in solution and in cells. While TRAX exerts little effect on the membrane binding of PLCβ1, it does reduce the affinity of PLCβ1 for Gαq and inhibits the stimulation of PLCβ1 activity by Gαq. TRAX, a cytosolic protein that can localize to the nucleus, isinvolved in the down-regulation of protein expression by RNA interference. Our study shows that cytosolic PLCβ1 can drive TRAX out of the nucleus and reduce siRNA activity. Furthermore, activation of Gαq results in apparent displacement of cytosolic PLCβ1 from TRAX and concurrently allows TRAX to relocalize to the nucleus. Importantly we have found that increased cytosolic expression of PLCβ1 appears to reverse the siRNA-induced down-regulation of GAPDH. Our data suggests a potential link between Gαq activation, PLCβ1 localization and siRNA activity.