Nucleotide sequence of the 3'-terminal half of beet yellows closterovirus RNA genome: unique arrangement of eight virus genes.

The sequence of 6746 nucleotides representing the 3'-proximal half of the beet yellows closterovirus (BYV) genome was determined. In the direction 5' to 3', the sequence was composed of eight open reading frames (ORFs) potentially encoding proteins of 6.4K (ORF2), 65K (ORF3), 64K (ORF4), 24K (ORF5), 22K (ORF6), 20K (ORF7) and 21K (ORF8). An incomplete ORF, ORF1, encoded the C-terminal part of a putative RNA-dependent RNA polymerase, most closely related to polymerases of tricornaviruses; the putative product of ORF3, 65K, was found to be a homologue of the hsp70 family of cell heat-shock proteins. ORF2 potentially encoded a small hydrophobic 6.4K protein, apparently homologous to small hydrophobic proteins of potex- and carlaviruses. ORF6 encoded the viral coat protein, as indicated by its deduced Mr and amino acid composition. The products of ORFs 4, 5, 7 and 8 showed no significant similarities with protein sequences in the database and there are therefore no justifiable speculations concerning their possible functions. BYV RNA contains a 3'-terminal non-coding region of 181 nucleotides, with two stem-loop structures potentially folded within the 86 nucleotide sequence at the extreme 3' end. Analysis of the primary and secondary structure of this region together with the absence of aminoacylation and adenylylation in vitro showed that the BYV genome is devoid of a tRNA-like structure at its 3' end.