The virus encodes two structural proteins that make up the capsid. These proteins orchestrate systemic movement within host plants and transcytosis within aphids [11, 12, 13, 14] . The 22-24 kDa coat protein (CP) expressed from the viral open reading frame (ORF) 3 is the major capsid protein. Occasionally, readthrough translation of the CP stop codon results in the translational fusion of ORF3 with ORF5, resulting in the minor protein species component of the capsid called the readthrough protein (RTP). Virions can be assembled from the CP alone, but the RTP is required for luteovirid movement across the ASG as well as efficient systemic infection [13, 14, 15, 16, 17] . These activities in aphids and plants are regulated by virion topological features, specifically interactions between CP monomers and welldefined interfacial regions within the RTP [18] .