MXA GTPASE - OLIGOMERIZATION AND GTP-DEPENDENT INTERACTION WITH VIRALRNP TARGET STRUCTURES

MxA protein is an interferon-induced GTPase of human cells that inhibi ts the multiplication of several RNA viruses, including influenza viru ses and bunyaviruses. Studies on MxA transgenic mice have shown that M xA is a powerful antiviral agent in vivo. It has been suggested that t his cellular protein also protects humans from viral disease, but the mechanism(s) by which MxA exerts its antiviral action is still poorly understood. Using an in vitro cosedimentation assay, we now demonstrat e that MxA tightly interacts with components of the ribonucleoprotein complex of Thogoto virus, an influenza-like virus transmitted by ticks . This assay demonstrates for the first time a physical interaction be tween MxA GTPase and a viral target structure. It is based on three el ements, namely, highly active MxA GTPases as effector molecules, viral ribonucleoprotein particles as viral targets, and GTP gamma S as a st abilizing factor. Furthermore, using a simple nuclear translocation as say, we show that human MxA protein forms oligomers in vivo. This assa y provides a stringent test for tight association of partner molecules in intact mammalian cells. It not only will be useful for studying ph ysical interactions of MxA with partner molecules, but may also be app licable to other studies on protein-protein interactions in living cel ls. (C) 1998 Academic Press.