From the functional point of view, the viral IRESs vary in primary and higher order structures and in their requirements for canonical translation initiation factors and other cellular or viral proteins which often bind to IRES and facilitate translation initiation complex attachment. The RNA region mediating cap-independent internal binding of the ribosome to viral RNA within the 5′-UTR-and thus internal initiation of protein synthesis-is called Internal Ribosome Entry Site (IRES). A common feature of cap-independently translated viral RNAs is the long and highly structured 5′-UTR which mediates the translation initiation complex binding and catalyses the formation of a functional ribosome. poliovirus, human rhinovirus, foot-and-mouth disease virus-to shut off the host-cell protein synthesis and hence usurp the cellular translational machinery for the efficient synthesis of their own proteins. The alternative strategies of protein synthesis even allow some viruses-e.g. Some viruses, including several important pathogens of human and livestock, do not bear the methylguanosine cap moiety attached to the 5′ terminus of their RNAs and have evolved a different strategy which allows them to initiate the synthesis of viral proteins by the cap-independent pathway. This mode of initiation is called the cap-dependent translation initiation. Once attached to the cap, the translation initiation complex scans 5′-UTR to the first initiation codon, the complete ribosome is assembled and starts the nascent polypeptide synthesis. All the eukaryotic cellular mRNAs contain a cap-a methylated guanosine moiety attached to their 5′ terminus, which ensures mRNA stability, and which is recognized by the ribosomal translation initiation complex. Generally, translation of all eukaryotic mRNAs is initiated at their 5′-untranslated region (5′-UTR) by binding the initiation complex, comprising of a small ribosomal subunit, other protein factors and the initiator Met-tRNAi. The initiation of translation is a rate-limiting step of the ribosomal phase of protein synthesis, and thus it is not surprising that both the overall and the targeted control of translation initiation have been found to play an important role in many processes ranging from the embryonic development and control of malignancy, to cellular response to stress and different external or internal stimuli. The post-transcriptional control of gene expression is attracting more and more attention at the present time, being seen as a part of the whole process of protein synthesis where both fast and fine tuning of the expression of particular mRNA and control of the overall level of protein synthesis are possible. New data can be submitted through the publicly available web-based interface at and are curated by a team of lab-experienced biologists. The annotated data in IRESite are bound to mostly complete, full-length mRNA, and whenever possible, accompanied by original plasmid vector sequences. Special care is given to the annotation of promoter-like regions. Furthermore, the site presents the known similarities to rRNA sequences as well as RNA–protein interactions. the nature of an IRES element, its functionality/defectivity, origin, size, sequence, structure, its relative position with respect to surrounding protein coding regions, positive/negative controls used in the experiment, the reporter genes used to monitor IRES activity, the measured reporter protein yields/activities, and references to original publications as well as cross-references to other databases, and also comments from submitters and our curators. Currently, IRESite presents up to 92 biologically relevant aspects of every experiment, e.g. Later on, they were also discovered in 5′-untranslated regions of some eukaryotic mRNA molecules. IRES elements were originally found in eukaryotic viruses hijacking initiation of translation of their host. IRESite is an exhaustive, manually annotated non-redundant relational database focused on the IRES elements (Internal Ribosome Entry Site) and containing information not available in the primary public databases.
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