IRES-Dependent Second Gene Expression Is Significantly Lower Than Cap-Dependent First Gene Expression in a Bicistronic Vector

• DOI: 10.1006/mthe.2000.0050
• Publication Date: 2002-09-18T19:46:43Z
• Authors: Hiroyuki Mizuguchi; Zhili Xu; Akiko Ishii-Watabe; Eriko Uchida; Takao Hayakawa
• Keywords: Chloramphenicol O-Acetyltransferase; RNA Caps; 0301 basic medicine; Genetic Vectors; Gene Expression; CHO Cells; Mice; 03 medical and health sciences; L Cells; Cricetinae; Drug Discovery; Genetics; Animals; Humans; Encephalomyocarditis virus; Luciferases; Molecular Biology; Pharmacology; Gene Transfer Techniques; Alkaline Phosphatase; Genes; Liver; Molecular Medicine; 5' Untranslated Regions; HeLa Cells; Plasmids

The internal ribosome entry site (IRES) has been widely used to coexpress heterologous gene products by a message from a single promoter. However, little is known about the efficiency of IRES-dependent second gene expression in comparison with that of first gene expression. This study was undertaken to characterize the relative expression of IRES-dependent second gene in a bicistronic vector, which was derived from the 5' untranslated regions of the encephalomyocarditis virus (EMCV). IRES-dependent second gene expression was compared with cap-dependent first gene expression in several cultured cell lines and in mouse liver in vivo. The expression of the IRES-dependent second gene ranged from 6 to 100% (in most cases between 20 and 50%) that of the first gene. Second gene expression in a plasmid without the IRES was 0.1-0.8% (with some exceptions) that of the first gene. These findings have important implications for the use of IRES, i.e., care should be taken regarding the decreased capacity of IRES-dependent downstream gene expression as well as in determining which gene should be positioned as the first or second gene in a bicistronic vector.