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In eukaryotes, IRES sequences aid the recruitment of factors needed for translation to occur, enabling protein production independent of 5′ capped mRNA. Many patents and commercially available plasmids exploit their properties for polycistronic expression of recombinant proteins. However, these applications have been restricted to eukaryotic organisms, since it was thought that elements of this origin were essential for their activity. Here, using two tricistronic vectors designed for expression in mammalian hosts, we present evidence of EMCV IRES activity in prokaryotes. This finding enables the development of new and more versatile plasmid vectors for the production of recombinant proteins in multiple hosts from a single construct. Additionally, it provides new hints for the elaboration of alternative models describing the molecular mechanism of EMCV IRES mediated translation, in the absence of eukaryotic elements that were considered indispensable for its function. [ABSTRACT FROM AUTHOR]

To determine whether 2A protease of the enterovirus genus with type I internal ribosome entry site (IRES) effect on the viral replication of type II IRES, coxsackievirus B3(CVB3)-encoded protease 2A and encephalomyocarditis virus (EMCV) IRES (Type II)-dependent or cap-dependent report gene were transiently co-expressed in eukaryotic cells. We found that CVB3 2A protease not only inhibited translation of cap-dependent reporter genes through the cleavage of eIF4GI, but also conferred high EMCV IRES-dependent translation ability and promoted EMCV replication. Moreover, deletions of short motif (aa13–18 RVVNRH, aa65–70 KNKHYP, or aa88–93 PRRYQSH) resembling the nuclear localization signals (NLS) or COOH-terminal acidic amino acid motif (aa133–147 DIRDLLWLEDDAMEQ) of CVB3 2A protease decreased both its EMCV IRES-dependent translation efficiency and destroy its cleavage on eukaryotic initiation factor 4G (eIF4G) I. Our results may provide better understanding into more effective interventions and treatments for co-infection of viral diseases. [ABSTRACT FROM AUTHOR]

Highlights: [•] Subtle alterations of the EMCV IRES can drastically reduce second cistron expression. [•] The EMCV IRES can mediate much higher expression than the VCIP and Gtx IRESes. [•] A cloning-friendly variation of the EMCV IRES performs comparably with the wild type element. [ABSTRACT FROM AUTHOR]

Abstract: Picornaviruses and other positive-strand RNA viruses like hepatitis C virus (HCV) enter the cell with a single RNA genome that directly serves as the template for translation. Accordingly, the viral RNA genome needs to recruit the cellular translation machinery for viral protein synthesis. By the use of internal ribosome entry site (IRES) elements in their genomic RNAs, these viruses bypass translation competition with the bulk of capped cellular mRNAs and, moreover, establish the option to largely shut-down cellular protein synthesis. In this review, I discuss the structure and function of viral IRES elements, focusing on the recruitment of the cellular translation machinery by the IRES and on factors that may contribute to viral tissue tropism on the level of translation. [Copyright &y& Elsevier]

Abstract: We compared the effects of polypyrimidine tract-binding protein (PTB) on hepatitis C virus (HCV genotype IIa), encephalomyocarditis virus (EMCV) and poliovirus internal ribosome entry site (IRES) activities in vitro. It bound strongly to EMCV IRES, but weakly to PV and HCV RNAs. PV IRES showed the strongest dependency to PTB and it showed less than one-tenth of IRES activity after the immuno-depletion of PTB from HeLa S10 lysate with pre-coated anti-PTB IgG beads, comparing to the normal IgG beads-treated S10 lysate. EMCV IRES activity was approximately 40% of that of normal control after PTB depletion. Especially, HCV IRES activity was approximately 95%, and most weekly affected by the depletion of PTB. Repletion of PTB to depleted S10 lysate restored activities of PV and EMCV IRESs. The data suggest that PTB plays an important role in picornaviral IRESs, but not in HCV IRES. [Copyright &y& Elsevier]

Abstract: Here we describe a system for promoterless analysis of putative internal ribosome entry site (IRES) elements using an alphavirus (family Togaviridae) replicon vector. The system uses the alphavirus subgenomic promoter to produce transcripts that, when modified to contain a spacer region upstream of an IRES element, allow analysis of cap-independent translation of genes of interest (GOI). If the IRES element is removed, translation of the subgenomic transcript can be reduced >95% compared to the same transcript containing a functional IRES element. Alphavirus replicons, used in this manner, offer an alternative to standard dicistronic DNA vectors or in vitro translation systems currently used to analyze putative IRES elements. In addition, protein expression levels varied depending on the spacer element located upstream of each IRES. The ability to modulate the level of expression from alphavirus vectors should extend the utility of these vectors in vaccine development. [Copyright &y& Elsevier]