Mushroom bacilliform virus RNA: the initiation of translation at the 5' end of the genome and identification of the VPg.

Mushroom bacilliform virus (MBV) is often found in cultivated mushrooms (Agaricus bisporus) with La France disease. MBV has a 4-kb ssRNA genome of positive-sense encoding four major open reading frames (ORFs). The arrangement of ORFs at the 5' end of the genome and the deduced amino-acid sequences of two of the putative gene products (protease and RNA-dependent RNA polymerase) show remarkable similarity to some plant viruses, particularly subgroup II luteoviruses. We show that this similarity extends to the translation strategy at the 5' end of the genome, the presence of a genome-linked protein (VPg), and the location of the VPg downstream of the protease motifs in the polypeptide encoded by ORF2.