Identification of a protein linked to the genomic and subgenomic mRNAs of feline calicivirus and its role in translation.

125I protein labelling of oligo(dT)-selected RNA from feline calicivirus (FCV)-infected cells revealed that the genomic and 2.4 kb subgenomic RNAs of FCV are linked to a 15 kDa protein (VPg). Proteinase K treatment of FCV RNA, to remove VPg, led to a decrease in the translatability of the RNA, but there was no obvious change in the site of RNA initiation. Addition of the cap analogue 7-methylGTP to in vitro translations had no effect on the translation of FCV RNA, suggesting that FCV RNA is translated by a cap-independent mechanism. Further evidence that FCV RNA is translated by an unusual mechanism was obtained by translating FCV RNA in vitro at a range of K+ concentrations. FCV RNA was able to direct translation at K+ concentrations at which cellular RNA translation was inhibited.