THE 3'-UNTRANSLATED REGION OF ALFALFA MOSAIC-VIRUS RNA-3 CONTAINS AT LEAST 2 INDEPENDENT BINDING-SITES FOR VIRAL COAT PROTEIN

The 3'-termini of the three genomic RNAs of alfalfa mosaic virus conta in a common sequence of 145 nucleotides (nt) with a specific binding s ite far coat protein (CP). This sequence consists of several stem/loop structures interspersed with single-stranded AUGC-motifs; in RNA 3 th is folding pattern is extended to a region upstream of the homologous sequence. By band-shift assays a minimum of two specific binding sites for CP were identified near the 3'-end of RNA 3. Site 1 consists of t he region between nt 11 and 127 from the 3'-end and contains two AUGC- motifs. Site 2 is located between nt 133 and 208 from the 3'-end in a sequence that is largely unique to RNA 3 and contains also two AUGC-mo tifs. Deletion studies revealed that the two sites could bind CP indep endently of each other and permitted the identification of sequence el ements that are essential for the activity of each site. By site-direc ted mutagenesis it was shown that the AUGC-motifs are important for bi nding of CP to both sites. These binding sites may play a role in the phenomenon that each genomic RNA has to be complexed with a few CP mol ecules to initiate infection. Later in the replication cycle they may act as origins for the assembly of virus particles.