Alfalfa Mosaic Virus

Abstract

Alfalfa mosaic virus (AMV) is the type species of the genus Alfamovirus in the family Bromoviridae. In contrast to viruses from other genera in this family, the three genomic RNAs of viruses from the genera Alfamovirus and Ilarvirus require binding of a few molecules of coat protein (CP) to the 3′ end of the viral RNAs for efficient initiation of infection. The 3′ termini of AMV RNAs can adopt two mutually exclusive structures. One of these represents a strong binding site for CP, the other resembles the tRNA-like structure (TLS) in the RNAs of CP-independent viruses in the family Bromoviridae. Binding of CP to the 3′ end of AMV RNAs strongly stimulates translational efficiency of the RNAs in plant cells. Similar to the poly(A)-binding protein (PABP), AMV CP interacts with the eIF4G subunit of the eIF4F complex of plant initiation factors. Polyadenylation of AMV RNAs permits CP-independent initiation of infection. These data indicate that CP stimulates AMV infection by mimicking the function of PABP in translation of cellular mRNA. The 3′ terminal TLS conformation of AMV RNAs is required for minus-strand promoter activity. A conformational switch at the 3′ end of AMV RNAs has been proposed to regulate viral translation and replication.