Abstract
BackgroundBovine viral diarrhea virus (BVDV) is the prototype representative of the pestivirus genus in the Flaviviridae family. It has been shown that the initiation of translation of BVDV RNA occurs by an internal ribosome entry mechanism mediated by the 5' untranslated region of the viral RNA [1]. The 5' and 3' boundaries of the IRES of the cytopathic BVDV NADL have been mapped and it has been suggested that the IRES extends into the coding of the BVDV polyprotein [2]. A putative pseudoknot structure has been recognized in the BVDV 5'UTR in close proximity to the AUG start codon. A pseudoknot structure is characteristic for flavivirus IRESes and in the case of the closely related classical swine fever virus (CSFV) and the more distantly related Hepatitis C virus (HCV) pseudoknot function in translation has been demonstrated.ResultsTo characterize the BVDV IRESes in detail, we studied the BVDV translational initiation by transfection of dicistronic expression plasmids into mammalian cells. A region coding for the amino terminus of the BVDV SD-1 polyprotein contributes considerably to efficient initiation of translation. The translation efficiency mediated by the IRES of BVDV strains NADL and SD-1 approximates the poliovirus type I IRES directed translation in BHK cells. Compared to the poliovirus IRES increased expression levels are mediated by the BVDV IRES of strain SD-1 in murine cell lines, while lower levels are observed in human cell lines. Site directed mutagenesis revealed that a RNA pseudoknot upstream of the initiator AUG is an important structural element for IRES function. Mutants with impaired ability to base pair in stem I or II lost their translational activity. In mutants with repaired base pairing either in stem 1 or in stem 2 full translational activity was restored. Thus, the BVDV IRES translation is dependent on the pseudoknot integrity. These features of the pestivirus IRES are reminiscent of those of the classical swine fever virus, a pestivirus, and the hepatitis C viruses, another genus of the Flaviviridae.ConclusionThe IRES of the non-cytopathic BVDV SD-1 strain displays features known from other pestivirus IRESes. The predicted pseudoknot in the 5'UTR of BVDV SD-1 virus represents an important structural element in BVDV translation.
Highlights
The pestiviruses like bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV) and border disease virus (BDV) are the causative agents of economically important diseases of cattle, pigs and sheep
We have stably transfected into BHK cells expression plasmids pSBCSNADLLUC and pSBCSSD1LUC which carry the genes for the secreted form of the alkaline phosphatase (SEAP) and the firefly luciferase as reporters and the complete Bovine viral diarrhea virus (BVDV) 5'UTR (NADL strain or SD-1-strain, respectively) as intercistronic region
For evaluation of the BVDV internal ribosomal entry site (IRES) strength pSBCSdeltapoLUC and pSBC-SEAPPolio-LUC were chosen which are similar dicistronic devoid of any IRES or containing the poliovirus type IRES which is a strong mediator of internal initiation of translation [17]
Summary
The pestiviruses like bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV) and border disease virus (BDV) are the causative agents of economically important diseases of cattle, pigs and sheep. The HCV IRES as well as the CSFV IRES contain a functional RNA pseudoknot structure upstream of the polyprotein initiation site that is indispensable for internal initiation of translation [3,1214]. We provide evidence that the BVDV strain SD-1 IRES translational efficiency is increased by BVDV N-terminal non-coding region and contains a RNA pseudoknot structure that is indispensable for IRES function. These features exhibit remarkable similarity to the IRES of HCV and are not common with the IRESes of picornaviruses represented by the cardioviruses or enteroviruses, emphasizing that BVDV SD-1 IRES matches well into this distinct group of internal ribosomal landing pads. A pseudoknot structure is characteristic for flavivirus IRESes and in the case of the closely related classical swine fever virus (CSFV) and the more distantly related Hepatitis C virus (HCV) pseudoknot function in translation has been demonstrated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
