Mechanism of Interferon Action: eIF-2α Phosphatase in Interferon-treated Mouse Fibroblasts is Double-stranded RNA Independent

The effect of double-stranded RNA on the dephosphorylation of purified, ³²P-labeled eIF-2 was examined in cell-free extracts prepared from interferon-treated mouse L₉₂₉ cells. Dephosphorylation of the α subunit of eIF-2 occurred at comparable rates in the presence and in the absence of reovirus dsRNA. By contrast, the β subunit of eIF-2 was not dephosphorylated to any significant extent in either the presence or the absence of dsRNA. These results indicate that the enhanced phosphorylation of eIF-2α observed in IFN-treated systems in the presence of double-stranded RNA (dsRNA) is indeed caused by an activation of a protein kinase rather than to an inhibition of a phosphoprotein phosphatase by the dsRNA.