Internal ribosome entry sites of viral and cellular RNAs

In recent years mechanism of internal initiation of translation in eukaryotic cells commands the attention of molecular biologists in increasing frequency. Ten years ago, experiments with picornaviruses demonstrated the ability of 40S ribosomal subunits to bind to nucleotide sequences localized far from the 5' ends of RNA molecules, and since then numerous viral and even cellular RNAs were shown to be capable of internal initiation of translation. In the present survey, data on the localization, structure, and functional load of these internal ribosome entry sites (IRES elements) of viral and cellular RNAs, as well as on proteins capable of strong and highly specific binding to IRES elements, are discussed. A conclusion is that a unified model of structure and functioning of viral and cellular IRES elements cannot be suggested.