Expression of alfalfa mosaic virus RNA 4 cDNA transcripts in vitro and in vivo

Copies of alfalfa mosaic virus (AMV) RNA 4 synthesized by transcription in vitro were shown to be biologically active in protoplasts when inoculated together with a mixture of AMV RNAs 1, 2, and 3. A 5' cap was essential for activity, whereas 15 nonviral nucleotides at the 5' end of the RNA transcripts did not detectably affect activity. Transcripts that terminated 65 nucleotides from the 3' end of the coding region and transcripts that lacked all or part of the 3'-noncoding region were effective messengers in a wheat germ cell-free translation system. None of the incomplete transcripts, however, were as biologically active in protoplasts or in Xenopus laevis oocytes as were complete transcripts. This suggests that the 3' end of RNA 4 is involved in translational stability.