Structure of the glycoprotein gene of sonchus yellow net virus, a plant rhabdovirus

Abstract

The nucleotide sequence of the glycoprotein (G) gene of sonchus yellow net virus (SYNV), a plant rhabdovirus, was determined from viral genomic and mRNA cDNA clones. The G cistron is 2045 nucleotides (nt) long and the G protein mRNA open reading frame (ORF), as determined from the cDNA sequence, contains 1896 nt and encodes a protein of 632 amino acids. Immunoblots with antibodies elicited against the purified glycoprotein from virus particles reacted with a fusion protein produced in Escherichia coli, indicating that the cloned ORF encodes the G protein. The 5′ end of the G protein mRNA corresponds to nt 5111, relative to the 3′ end of the viral (minus sense) genome, as determined by primer extension from mRNA isolated from infected plants, and extends to nt position 7155 on the genomic RNA. A 34-nt untranslated 5′ leader sequence and a 115-nt untranslated 3′ end flank the ORF on the mRNA. The gene junctions on either side of the G gene on the genomic RNA are identical to those previously described for other SYNV genes and are similar to sequences separating genes of animal rhabdoviruses. The predicted molecular weight of the G protein is 70,215 Da, a value less than the 77,000 Da estimated for the glycosylated G protein from virus particles. The deduced amino acid sequence of the SYNV G protein shares little direct relatedness with the G proteins of other rhabdoviruses, but appears to contain a similar signal sequence, a transmembrane anchor domain, and glycosylation signals. In addition, the SYNV G protein contains a putative nuclear targeting site near the carboxy terminus, which may be involved in transit to the nuclear membrane prior to morphogenesis.