The complete nucleotide sequence of tobacco necrosis virus strain D

Abstract

The complete sequence of the RNA genome of tobacco necrosis virus strain D (TNV-D) consisting of 3759 nucleotides has been determined. The positive strand contains five open reading frames (ORFs). The 5'-proximal ORF encodes a 22K protein terminating with an amber codon which may be read through to produce a 82K protein (p82). Two small centrally located ORFs each encode two out-of-frame 7K proteins (p7a and p7b). The 3'-proximal ORF encodes the 29K coat protein (CP), the N terminus of which has been sequenced directly. The genomic organization of TNV-D is very similar to that of TNV-A but differs in the placement of the p7a ORF, which does not overlap the p82 ORF in TNV-D, and in the absence of an ORF downstream of the CP gene in TNV-D. The p82 ORF shows extensive sequence similarity with the putative polymerases of the carmovirus group. This ORF is also as closely related to the corresponding ORF of TNV-A as it is to the corresponding ORF of the tombusvirus cucumber necrosis virus. The amino acid sequence of the TNV-D CP gene is similar to both the TNV-A and southern bean mosaic virus CP genes. Of the two p7 ORFs, p7a exhibits amino acid sequence similarity with corresponding proteins from TNV-A, melon necrotic spot virus, carnation mottle virus, turnip crinkle virus and maize chlorotic mottle virus, whereas the p7b ORF appears to be unique to TNV-A and TNV-D. Only the 3'-terminal three nucleotides of TNV-D genomic RNA are identical to the 3'-terminal nucleotides of the TNV satellite virus.