Nucleotide sequence of the 3'-terminal region of potato virus YN RNA

The sequence of the 3'-terminal 1611 nucleotides of the genome of the tobacco veinal necrosis strain of potato virus Y (PVYN) was determined. The sequence revealed an open reading frame of 1285 nucleotides, of which the start was not identified, and an untranslated region of 316 nucleotides upstream of a poly(A) tract. Comparison of the open reading frame with the amino-terminal sequence of the viral coat protein enabled mapping of the start of the coat protein at amino acid -267, and indicated that maturation of this protein requires proteolytic processing from a larger polyprotein precursor at a glutamine/glycine dipeptide sequence. The coat protein of PVYN displayed significant (51 to 63%) sequence homology to the coat proteins of four other potyviruses, tobacco etch virus, tobacco vein mottling virus, plum pox virus and sugarcane mosaic virus. Even higher sequence homology (91%) was detected with the coat protein of a fifth potyvirus, pepper mottle virus (PeMV). This homology was of the same level as found between the coat proteins of PVYN and a second strain of this virus, PVYD. Since, moreover, PVYN and PeMV were the only potyviruses displaying homology in the 3'-terminal, non-translated regions of their genomes, we conclude that PeMV should be regarded as a strain of PVY.