Guanine-Nucleotide Exchange Factor RCC1 Facilitates a Tight Binding between the Encephalomyocarditis Virus Leader and Cellular Ran GTPase

Abstract

The leader (L) protein of encephalomyocarditis virus (EMCV) shuts off host cell nucleocytoplasmic trafficking (NCT) by inducing hyperphosphorylation of nuclear pore proteins. This dramatic effect by a nonenzymatic protein of 6 kDa is not well understood but clearly involves L binding to cellular Ran GTPase, a critical factor of active NCT. Exogenous GDP and GTP are inhibitory to L-Ran binding, but the guanine-nucleotide exchange factor RCC1 can relieve this inhibition. In the presence of RCC1, L binds Ran with a K D (equilibrium dissociation constant) of ∼3 nM and reaches saturation within 20 min. The results of fluorescently tagged nucleotide experiments suggest that L-Ran interactions affect the nucleotide-binding pocket of Ran.