Amino acids of alfalfa mosaic virus coat protein that direct formation of unusually long virus particles

V Thole, R Miglino and JF Bol Institute of Molecular Plant Sciences, Gorlaeus Laboratories, Leiden University, The Netherlands. In contrast to most alfalfa mosaic virus (AMV) strains (YSMV, S, M and 425), AMV strains VRU and 1 5/64 can form abnormally long virus particles, an ability which has been linked to the coat protein (CP). In order to study this phenomenon, the CP-encoding RNAs 3 of AMV strains VRU and 1 5/64 were cloned and fully sequenced. Comparative sequence analyses of AMV RNA 3 sequences derived from different strains revealed two non-conservative amino acid substitutions, Ser65 and Leu175, which occur exclusively in the closely related VRU- and 15/64- CPs. When these amino acid alterations were introduced into the CP of AMV strain 425 unusually long virus particles were assembled. This confirms that amino acids Ser66 and Leu175 of the CPs of AMV strains VRU and 15/64 are involved in the formation of tubular virus particles.