Biologically active transcripts of cloned DNA of the coat protein messenger of two plant viruses

To initiate infection, a mixture of the three genomic RNAs of alfalfa mosaic virus (AIMV) has to be supplemented with a small amount of coat protein or RNA 4, the subgenomic messenger for coat protein. The possibility to replace RNA 4 in the inoculum by in vitro synthesized transcripts of a cloned DNA copy of the coat protein cistron was investigated using the SP6 transcription system. Transcripts with or without the cap structure m(7)G(5')ppp(5')G were both translated in vitro in viral coat protein, but only capped transcripts yielded an infectious mixture when added to the AIMV genomic RNAs. This indicates that the cap structure is essential to the in vivo translatin of RNA 4. Similar results were obtained with RNAs transcribed in vitro from a DNA copy of the putative coat protein cistron of tobacco streak virus (TSV). re]19850822 rv]19851203 ac]19860114.