The 2–5A system is an interferon-regulated antiviral RNA decay pathway present in cells of higher vertebrates. Two enzymes are essential, a 2–5A synthetase which produces 5′-phosphorylated, 2′,5′-linked oligoadenylates (2–5A) in response to doublestranded RNA, and the 2–5A-dependent RNase L. To determine if these human proteins would be functional in plants, we expressed the human cDNAs for a 2–5A synthetase and RNase L in separate tobacco plants. Both proteins were enzymatically active in extracts of transgenic plants while such activities were not detected in the control plants. Furthermore, activation by 2–5A of RNase L in the transgenic plant leaves was shown to cause degradation of ribosomal RNA. The requirement for both the synthetase and RNase L for antiviral activity was underscored by the observations that expression of human RNase L alone or 2–5A-synthetase alone was insufficient to protect plants against either tobacco etch virus or tobacco mosaic virus.
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