Beet soil-borne virus RNA 1: genetic analysis enabled by a starting sequence generated with primers to highly conserved helicase-encoding domains.

The complete sequence of the 5834 nucleotides of RNA 1 of beet soil-borne furovirus (BSBV, Ahlum isolate) was determined using a PCR product obtained with primers to highly conserved coding regions for helicase-like proteins in RNA 1 of furo-, hordei- and tobraviruses as a starting sequence. Unknown parts of the sequence upstream and downstream of this starting sequence were amplified by means of RT-PCR techniques using combinations of specific and random primers. BSBV RNA 1 contains one large ORF for a readthrough protein with a molecular mass of 204 kDa (204K protein) which is interrupted internally by a UAA stop codon terminating the coding region for a protein of 145 kDa (145K protein). The N- and C-terminal parts of the 145K protein and the readthrough domain of the 204K protein contain methyltransferase, helicase and RNA-dependent RNA polymerase motifs, respectively. Unlike other furo- and tobraviruses BSBV contains no further genes on its RNA 1.