Cloning and nucleotide sequence of the capsid protein and the nuclear inclusion protein (NIb) of potato virus A.

The sequence of the 3'-terminal 2597 nucleotides of potato virus A (PVA) genome has been determined from cDNA clones. An open reading frame was identified and potentially encodes a large polyprotein containing 789 amino acid residues. This large open reading frame was found to have a high similarity to the nuclear inclusion protein (NIb) and the capsid protein (CP) genes of several potyviruses. The data suggest that the PVA NIb and CP are products arising from the maturation of the large polyprotein as observed for other potyviruses. Putative cleavage sites corresponded to consensus sequences NIa/NIb and NIb/CP, respectively, of other potyviruses. The NIb (putative RNA polymerase) and CP are expected to be 516 and 269 amino acid residues (M(r) of 58,939 and 30,094), respectively. The non-coding region is 227 nucleotides long, rich in A and U and unlike other viruses. Furthermore, there are two AUG codons in frame in front of the capsid protein gene suggesting an alternative mode for the capsid protein expression.