Isolated Acetabularia crenulata nuclei were injected with Mengo virus RNA solution and then implanted into anucleate posterior Acetabularia mediterranea cell fragments or fused with Acetabularia ryukyuensis cytoplasts. The injected animal virus RNA was actively translated in the plant cell cytoplasm. Mengo virus proteins were detected and localized in Acetabularia cytoplasts by use of an immunofluorescence method on the first to fifth day after injection.