The novel picornavirus Equine rhinitis B virus contains a strong type II internal ribosomal entry site which functions similarly to that of Encephalomyocarditis virus.

The research explores how the Equine rhinitis B virus (ERBV) uses a type II internal ribosome entry sequence (IRES) to initiate translation in a way similar to the Encephalomyocarditis virus (EMCV). The study identifies that the ERBV IRES and EMCV IRES can compete for translation factors thus making ERBV IRES a possibly strong inducer of translation.

Introduction

• The research pivots on the Equine rhinitis B virus (ERBV), a recent addition to the Erbovirus genus in the Picornaviridae family.
• The ERBV has distant relations with the Cardiovirus and Aphthovirus genera that utilize a type II internal ribosome entry sequence (IRES) to initiate the translation process. The research demonstrates that ERBV also contains a similar type II IRES.

Methodology

• The researchers used bicistronic plasmids to analyze the function of the ERBV IRES by transfecting them into BHK-21 cells and utilizing in vitro transcription and translation in rabbit reticulocyte lysates.
• A region spanning nucleotides 189-920 downstream of the poly(C) tract was found to be necessary for maximal translation. This region includes stem-loops H-L and four additional upstream stem-loops.
• Nucleotide 904 was identified as the second of three in-frame AUG codons placed after the polypyrimidine tract (nucleotides 869-880).
• Through site-directed mutagenesis, it was identified that AUG2 is the key initiation codon despite the proper positioning of AUG1 located 16 nucleotides downstream of the polypyrimidine tract.

Results

• In IRES competition experiments, the ERBV IRES was found to compete robustly for translation factors with the IRES from the Encephalomyocarditis virus (EMCV). This was verified in both in vivo and in vitro assays.
• The study reveals that the ERBV IRES functions similarly to the EMCV IRES, suggesting potential comparable usage in mammalian expression systems.
• Comparison of several IRESs strength indicates that the ERBV IRES, much like the EMCV IRES, is a potent inducer of translation.

Conclusion

• This study sheds light on the similarities between the ERBV and EMCV viruses,
  particularly their manner of initiating translation through the type II IRES. Moreover, the study indicates that the ERBV IRES can compete robustly with the EMCV IRES for translation factors.
• The findings suggest that the ERBV IRES could be a strong inducer of translation with potential use in mammalian expression systems, similar to the EMCV IRES.