Internal ribosome entry sites (IRESs): reality and use

• Published in: Transgenic research 1999-06, Vol.8 (3), p.157-177
• Main Authors: HOUDEBINE, L. M, ATTAL, J
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biotechnology; Cistrons; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation; Genetic engineering; Genetic technics; Genetic Vectors; Humans; Intercistronic region; internal ribosome entry sites; Laboratories; Life Sciences; Methods. Procedures. Technologies; Molecular and cellular biology; Molecular genetics; mRNA; Nucleotides; Peptide Initiation Factors - metabolism; Protein Biosynthesis; Proteins; Recruitment; Ribonucleic acid; Ribosomes; Ribosomes - genetics; Ribosomes - metabolism; RNA; RNA Caps - chemistry; RNA Caps - genetics; RNA Caps - metabolism; RNA, Messenger - chemistry; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Viral - genetics; RNA, Viral - metabolism; Scanning; Translation; Translation. Translation factors. Protein processing; Vectors (cloning, transfer, expression). Insertion sequences and transposons
• ISSN: 0962-8819; 1573-9368
• DOI: 10.1023/A:1008909908180

IRESs are known to recruit ribosomes directly, without a previous scanning of untranslated region of mRNA by the ribosomes. IRESs have been found in a number of viral and cellular mRNAs. Experimentally, IRESs are commonly used to direct the expression of the second cistrons of bicistronic mRNAs. The mechanism of action of IRESs is not fully understood and a certain number of laboratories were not successful in using them in a reliable manner. Three observations done in our laboratory suggested that IRESs might not work as functionally as it was generally believed. Stem loops added before IRESs inhibited mRNA translation. When added into bicistronic mRNAs, IRESs initiated translation of the second cistrons efficiently only when the intercistronic region contained about 80 nucleotides, and they did not work any more effectively with intercistronic regions containing at least 300-400 nucleotides. Conversely, IRESs inserted at any position into the coding region of a cistron interrupted its translation and initiated translation of the following cistron. The first two data are hardly compatible with the idea that IRESs are able to recruit ribosomes without using the classical scanning mechanism. IRESs are highly structured and cannot be scanned by the 40S ribosomal subunit. We suggest that IRESs are short-circuited and are essentially potent stimulators favoring translation in particular physiological situations.