Translation of the Minor Capsid Protein of a Calicivirus Is Initiated by a Novel Termination-dependent Reinitiation Mechanism

Abstract

Caliciviruses represent a family of positive strand RNA viruses responsible for a variety of syndromes in man and animals. VP10, a minor structural protein of the calicivirus rabbit hemorrhagic disease virus, is encoded in the small 3-terminal open reading frame (ORF) 2 and is translated with an efficiency of ϳ20% of the preceding ORF1. The presence of the ORF1 termination codon is crucial for VP10 expression. Translation of VP10 starts at an AUG codon located at positions ؊5 to ؊3 of the ORF1 termination codon. However, VP10 was also expressed in the absence of an AUG initiation codon. The majority of ORF1 could be deleted or replaced by different sequences without significant influence on VP10 expression as long as translation terminated at the given position. The RNA sequence of the 3-terminal 84 nucleotides of ORF1 but not the encoded peptide was found to be crucial for VP10 expression. In contrast, nearly the entire ORF2 could be replaced by a foreign sequence without abrogation of its translation. Accordingly, VP10 is expressed in a translation termination/reinitiation process that is particular because it is independent of an AUG translational start codon and requires the presence of a sequence element upstream of the initiation site.

Coupled Translation of the Respiratory Syncytial Virus M2 Open Reading Frames Requires Upstream Sequences

“…Thus, the majority of M2-1 ORF participates in the process of coupled translation, with some segments more important than others. This differs significantly from the findings for the RHDV calicivirus subgenomic mRNA where only 84 nucleotides of the sequence upstream of the overlap region recovered ϳ90% wild type expression levels of ORF2 (18).…”

“…1A), and Ahmadian et al (17) show that initiation of translation of the second, M2-2, ORF was coupled to termination of translation of the first ORF as moving the translational stop codon of the M2-1 ORF further downstream abrogated translation of the second ORF. A similar phenomenon was described for the subgenomic mRNA found in RHDVinfected cells where translation of ORF3 of the genome is coupled to termination of translation of the upstream ORF (18). In both cases, it was shown that the nucleotide sequence of the second downstream ORF was not essential for the process to occur because the virus ORF could be replaced with other sequences without an effect on the coupled translation (17,18).…”

“…A similar phenomenon was described for the subgenomic mRNA found in RHDVinfected cells where translation of ORF3 of the genome is coupled to termination of translation of the upstream ORF (18). In both cases, it was shown that the nucleotide sequence of the second downstream ORF was not essential for the process to occur because the virus ORF could be replaced with other sequences without an effect on the coupled translation (17,18). For the RSV study, the gene encoding bacterial chloramphenicol acetyltransferase (CAT) was substituted for the M2-2 gene (Fig.…”

A Bipartite Sequence Motif Induces Translation Reinitiation in Feline Calicivirus RNA

“…The biochemistry behind such a termination/reinitiation process is not fully understood. In two cases, the implication of upstream sequences has been reported although the function of these sequences is not known (24,25).…”

A DNA-launched reverse genetics system for rabbit hemorrhagic disease virus reveals that the VP2 protein is not essential for virus infectivity

“…The start codon for ORF2 is located at nt 7025 and shares a 17 nt overlap with ORF1, but has a 21 frame shift relative to the capsid ORF. RHDV ORF2 is 117 aa and encodes a polypeptide of 12.7 kDa (VP2), which is considered a component of RHDV virions (Wirblich et al 1996;Meyers et al, 2000;Meyers, 2003). VP2 is conserved throughout the caliciviruses, suggesting that it may play a role in virus replication or assembly.lack of reagents to detect ORF2 has hampered studies of the VP2 protein.…”