title: Translational efficiency of EMCV IRES in bicistronic vectors is dependent upon IRES sequence and gene location.
abstract: The internal ribosomal entry site (IRES)from encephalomyocarditis virus (EMCV) is a popular RNA element used widely in experimental and pharmaceutical applications to express proteins in eukaryotic cells or cell-free extracts. Inclusion of the wild-type element in monocistronic or bicistronic messenger RNAs (mRNAs) confers a high level of cap-independent translation activity to appropriately configured cistrons. The history of this element and the experimental consequences of sequence derivations inherent to commercial IRES vectors are less well known. Compared head-to-head with dual-luciferase reporter constructs, a native EMCV IRES in a bicistronic configuration directed 8- to 10-fold more protein than a similarly configured pIRES vector. It also produced nearly twice as much protein as pCITE-1, an early monocistronic iteration, harboring a suboptimal A7 sequence in a crucial structural motif The results indicate that investigators should be aware of and carefully report the sequence of their IRES in any comparative study. The preferred IRES (viral bases 273-845) and the minimum IRES (viral bases 400-836) for optimum activity are illustrated.
authors.affiliation: Institute of Molecular Virology, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Yury A
authors.initials: YA
authors.lastname: Bochkov
authors.forename: Ann C
authors.initials: AC
authors.lastname: Palmenberg
mesh_terms: D001483:Base Sequence; D004686:Encephalomyocarditis virus / Q000235:genetics*; D017930:Genes, Reporter; D005822:Genetic Vectors; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016366:Open Reading Frames; D010957:Plasmids / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D008156:Luciferases