Differential effects of two interferon-induced translational inhibitors on initiation of protein synthesis.

At least two different mechanisms for the inhibition of mRNA translation operate in extracts of interferon-treated L cells. One is mediated by an interferon-induced protein kinase which, when activated by double-stranded RNA and ATP, phosphorylates the small subunit of initiation factor eIF-2. Addition of the purified interferon-induced protein kinase to L cell extracts, strongly reduces the amount of methionyl-tRNA bound to 40-S ribosomal subunits. The second translational inhibition is due to the synthesis of (2'-5')oligo(adenylate) by interferon-induced enzyme E. The oligonucleotide in turn activates a ribonuclease F constitutively present in L cells. Addition of the purified nuclease with its oligonucleotide activator to L cell extracts produces a strong decrease in polyribosome formation and an accumulation of initiation complex. These experiments differentiate the effects of the two interferon-induced inhibitors on mRNA translation.