RNA-4A AND RNA-5 ARE PRESENT IN TOMATO ASPERMY VIRUS AND BOTH SUBGROUPS OF CUCUMBER MOSAIC-VIRUS

Primer extension analysis was used to determine the presence of RNAs 4 A and 5 in tomato aspermy virus (TAV) and both subgroups of cucumber m osaic virus (CMV). RNAs 4A and 5 were detected in TAV and all CMV stra ins (representative of both subgroups) that were analysed, except for one subgroup I CMV strain which lacked detectable RNA 5. In subgroup I I CMV strains the RNA 5 population was found to consist of two sequenc e variants. Comparison of the RNA 5 sequences from TAV and CMV indicat ed that TAV and subgroup II CMV RNA 5 share a much greater degree of s equence similarity than either has with subgroup I RNA 5. RNA 4A and t he encoded 2b protein appear to be unique to the cucumovirus genus of the tripartite viruses, which share an otherwise common genome structu re, and may have played a role in the evolutionary origin of this genu s.