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Abstract
Sequence variability was analysed in Central European isolates of potato virus S (PVS), which according to their inability to develop systemic infection in Chenopodium quinoa, resembled an ordinary strain of this virus. Nucleotide comparisons of eight experimental clones for the C-terminal part of the replicase, the coat protein, and the 1 l-kDa protein revealed 55, 47, and 13 variable sites, respectively. Because about 60-80% of base changes were fixed in the third triplet position, a high conservation of protein sequences and important domains, characteristic for the carlavirus group, was observed. A phylogenetic tree constructed for the coat protein amino acid sequences, showed more than 96.7% homology within the group of experimental PVS clones. The multiple sequence variants of PVS were detected for isolate Kobra using temperature-gradient gel electrophoresis of a coat-protein-derived 260-bp cDNA, suggesting a broad variability of PVS. The entire 3' terminal portion of PVS Kobra was reconstituted. A comparison of this sequence with an Andean PVS strain revealed 81.4% homology on a nucleotide level and some shifts in open reading frame patterns. The most significant differences between PVS Kobra and an Andean strain were found at the N-terminal regions of the 7-kDa protein, coat protein, and 1 l-kDa protein, suggesting that these proteins (encoded by the 3' region of the genome) could be responsible for the different levels of pathogenesis caused by these two PVS strains.