Minor component of the viral capsid involved in aphid transmission and virus accumulation in the host (PubMed:8623554). Required fro the virus to move through the aphid (PubMed:8623554). The RTD domain of the protein is exposed on the surface of the particle and determines the vector specificity and intestinal tropism in the aphid (By similarity). The N-terminus is highly basic like those of many plant virus capsid proteins (Probable). These regions may be involved in protein-RNA interaction (Probable). The RTD N-terminus is responsible for aphid transmission and aphid endosymbiont interaction (By similarity). The readthrough domain is required for transport of virus through membranes of the aphid salivary glands (PubMed:8623554). In virus particles, more than 200 amino acids are proteolytically cleaved releasing the C-terminus part of the RTD domain (Probable). The cleaved product remains attached to the virus particle (By similarity). This protein is translated as a fusion protein by episodic readthrough of the major coat protein termination codon. It is composed of the major capsid protein fused to a long C-terminal extension called the readthrough domain (RTD). Readthrough of the terminator codon TAG occurs between the codons for 200-Lys and 202-Val. Belongs to the luteoviruses readthrough protein family. Readthrough of an in-frame TAG stop codon in position 201 translated as Tyr.