Frog virus 3-induced translational shut-off: activation of an eIF-2 kinase in virus-infected cells

Abstract

Infection of susceptible fathead minnow or Friend erythroleukemia cells with either infectious or heat-inactivated frog virus 3 led to the rapid inhibition of cellular protein synthesis. As seen in other cells, translational shut-off was accompanied by the dissociation of polysomes, but not the degradation of irreversible inactivation of cellular mRNAs. In addition, lysates from cells infected with heat-inactivated FV3 showed a reduced capacity to synthesize protein and to form 43S pre-initiation complexes in vitro. These results indicate that the in vitro systems accurately reflected in vivo events, and suggest that translational shut-off occurred prior to the union of the 40S ribosomal subunit and the [eIF-2 . GTP . Met tRNA i] ternary complex. To determine the basis for the translational block, lysates from mock- and FV3-infected cells were assayed in vitro for their ability to phosphorylate the α subunit of eIF-2. In contrast to lysates from mock-infected cells, lysates from cells infected with heat-inactivated or infectious FV3 readily phosphorylated the α subunit of eIF-2. Since phosphorylation of the α subunit of eIF-2 inhibits its catalytic utilization during polypeptide chain initiation, these findings suggest that translational shut-off mediated by FV3 may be due to activation of a kinase that selectively phosphorylates this key initiation factor.