THE 3'-UNTRANSLATED REGION OF ALFALFA MOSAIC-VIRUS RNA3 CONTAINS A CORE PROMOTER FOR MINUS-STRAND RNA-SYNTHESIS AND AN ENHANCER ELEMENT

The 3' untranslated regions (UTRs) of the three genomic RNAs of alfalf a mosaic virus consist of a 3' homologous sequence of 145 nt and upstr eam unique sequences 18-34 nt in length. Mutations were made in the 3' UTR of a cDNA clone of RNA3. Point mutations in five AUGC motifs whic h interfere with specific binding of coat protein to the 3' UTR had no effect on template activity of RNA3 for minus-strand RNA synthesis in vitro by purified viral RNA-dependent RNA polymerase (RdRp). Deletion analysis showed that the 3' homologous sequence of 145 nt was suffici ent for a low level of template activity in the in vitro RdRp assay an d a similarly low level of RNA3 accumulation in plants. The presence o f an additional sequence of nucleotides 145-165 from the 3' end of RNA 3 enhanced template recognition by RdRp in vitro and accumulation of R NA3 in vivo to wild-type levels.