Conserved and variable elements in RNA genomes of potexviruses

The nucleotide sequences of genomic RNAs and predicted amino acid sequences of two strains of potato virus X and white clover mosaic potexvirus were compared to each other, and the proteins of different plus‐RNA‐containing plant viruses. The predicted non‐virion proteins of potexviruses have direct sequence homology and common structural peculiarities with those of several ‘Sindbis‐like’ plant viruses. The most conserved amino acid sequences were found to be located in the polypeptide encoded by the long 5′‐proximal open reading frame (ORF1). The putative polypeptide encoded by the ORF2 starting beyond the ORF1 stop codon is clearly related to the presumptive NTP‐binding domain of the ORF1‐coded polypeptide. These results suggest possible functions for all of the potexvirus proteins and also indicate that potexviruses have a genome organization which is considerably different from that of other plant viruses.