Reusken C B, Neeleman L, Bol J F
Institute of Molecular Plant Sciences, Gorlaeus Laboratories, Leiden University, The Netherlands.
Nucleic Acids Res. 1994 Apr 25;22(8):1346-53. doi: 10.1093/nar/22.8.1346.
The 3'-termini of the three genomic RNAs of alfalfa mosaic virus contain a common sequence of 145 nucleotides (nt) with a specific binding site for coat protein (CP). This sequence consists of several stem/loop structures interspersed with single-stranded AUGC-motifs; in RNA 3 this 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 the 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-motifs. Deletion studies revealed that the two sites could bind CP independently of each other and permitted the identification of sequence elements that are essential for the activity of each site. By site-directed mutagenesis it was shown that the AUGC-motifs are important for binding 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 molecules to initiate infection. Later in the replication cycle they may act as origins for the assembly of virus particles.
苜蓿花叶病毒三种基因组RNA的3'末端包含一段145个核苷酸（nt）的共同序列，带有衣壳蛋白（CP）的特异性结合位点。该序列由几个茎环结构穿插着单链AUGC基序组成；在RNA 3中，这种折叠模式延伸至同源序列上游的一个区域。通过凝胶迁移试验，在RNA 3的3'末端附近鉴定出至少两个CP特异性结合位点。位点1由3'末端第11至127位核苷酸之间的区域组成，包含两个AUGC基序。位点2位于3'末端第133至208位核苷酸之间，该序列在很大程度上是RNA 3特有的，也包含两个AUGC基序。缺失研究表明，这两个位点可彼此独立地结合CP，并有助于鉴定对每个位点活性至关重要的序列元件。通过定点诱变表明，AUGC基序对于CP与两个位点的结合都很重要。这些结合位点可能在每种基因组RNA必须与一些CP分子复合以启动感染的现象中发挥作用。在复制周期后期，它们可能充当病毒粒子组装的起始点。
