Dissecting the Initiation Factors Required for Translation Initiation on Feline Calicivirus RNA.

Caliciviruses are single-stranded positive-sense RNA viruses. The viral genome is polyadenylated at the 3' end and 7-8 kb in length. The 5' end of the genome does not possess a cap structure to direct translation of the mRNA. Instead, a viral protein VPg is present which has been demonstrated to act as a novel proteinaceous ‘cap-substitute’ to direct the translation of both the genomic and subgenomic RNAs. Initial work has shown that eIF4A is required for the translation of feline calicivirus (FCV) RNA. The aim of this study was to carry out further analysis of the initiation factors of the eIF4F cap binding complex (eIF4A, eIF4G, eIF4E and poly A binding protein-PABP) and their requirement translation of feline calicivirus (FCV) mRNA. We have developed a system to knock down eIF4AI expression in Crandell Rees Feline Kidney (CRFK) cells using siRNA, and have shown that this leads to an inhibition of virus translation and replication. We have also shown that eIF4AI binds to the FCV RNA and have determined the minimal binding site of eIF4AI on FCV RNA. As a second parameter of our study, we have also demonstrated the knock down of PABP expression in CRFK cells using siRNA and showed that this knockdown also leads to inhibition of FCV translation and replication. Finally we have shown that knockdown of eIF4GI in Human Embryonic kidney (HEK-293) cells using shRNA leads to inhibition of FCV protein synthesis and replication. On the basis of this research, we have proposed a model of the interactions of the FCV RNA with components of the eIF4F complex i.e., eIF4A, eIF4G and PABP. Furthermore, our model also suggests a possible mechanism for the switch from translation to replication of viral RNA late in infection.