The 5′ untranslated region is the region of an mRNA that is directly upstream from the initiation codon. This region is important for the regulation of translation of a transcript by differing mechanisms in viruses, prokaryotes and eukaryotes. While called untranslated, the 5′ UTR or a portion of it is sometimes translated into a protein product. This product can then regulate the translation of the main coding sequence of the mRNA. In many organisms, however, the 5′ UTR is completely untranslated, instead forming complex secondary structure to regulate translation.
An internal ribosome entry site, abbreviated IRES, is an RNA element that allows for translation initiation in cap-independent manner, as part of the greater process of protein synthesis. In eukaryotic translation, initiation typically occurs at the 5' end of mRNA molecules, since 5' cap recognition is required for the assembly of the initiation complex. The location for IRES elements is often in the 5'UTR, but can also occur elsewhere in mRNAs.
Eukaryotic translation is the biological process by which transfer RNA is translated into proteins in eukaryotes. It consists of four phases: gene regulation, elongation, termination, and recycling.
The bag-1 internal ribosome entry site (IRES) is a cis-acting element located in the 5 ' untranslated region of the BAG-1 protein mRNA. Its effects apoptosis through IRES mediated translation of the BAG-1 protein.
The c-myc internal ribosome entry site (IRES) is an RNA element present in the 5' UTR of the mRNA of C-myc and allows cap-independent translation. The mammalian c-myc gene is a proto-oncogene which is required for cell proliferation, transformation and death. c-myc mRNA has an alternative method of translation via internal ribosome entry where ribosomes are recruited to the IRES located in the 5' UTR thus bypassing the typical eukaryotic cap-dependent translation pathway.
The Cripavirus internal ribosome entry site is an RNA element required for the production of capsid proteins through ribosome recruitment to an intergenic region IRES.
The c-sis internal ribosome entry site (IRES) is a RNA element found in the 5' UTR of the PDGF beta chain gene. The internal ribosome entry site contains three modules that can individually mediate internal ribosome entry. However, the full length sequence is required for maximal IRES activity. It is thought that the three IRES elements are somehow responsive to cellular changes and act to regulate the level of translation.
The Epstein–Barr virus nuclear-antigen internal ribosome entry site is an internal ribosome entry site (IRES) that is found in an exon in the 5' untranslated region of the Epstein–Barr virus nuclear antigen 1 (EBNA1) gene. The EBNA IRES allows EBNA1 translation to occur under situations where initiation from the 5' cap structure and ribosome scanning is reduced. It is thought that the EBNA IRES is necessary for the regulation of latent-gene expression.
This family represents the internal ribosome entry site (IRES) of the hepatitis A virus. HAV IRES is a 450 nucleotide long sequence located in the 735 nt long 5’ UTR of Hepatitis A viral RNA genome. IRES elements allow cap and end-independent translation of mRNA in the host cell. The IRES achieves this by mediating the internal initiation of translation by recruiting a ribosomal 40S pre-initiation complex directly to the initiation codon and eliminates the requirement for eukaryotic initiation factor, eIF4F.
The Hepatitis C virus internal ribosome entry site, or HCV IRES, is an RNA structure within the 5'UTR of the HCV genome that mediates cap-independent translation initiation.
This family represents the Kaposi's sarcoma-associated herpesvirus (KSHV) internal ribosome entry site (IRES) present in the vCyclin gene. The vCyclin and vFLIP coding sequences are present on a bicistronic transcript and it is thought the IRES may initiate translation of vFLIP from this bicistronic transcript.
The L-myc internal ribosome entry site (IRES) is an RNA element present in the 5' UTR of the mRNA of L-myc that allows cap-independent translation. L-myc undergoes translation via the internal ribosome entry site and bypasses the typical eukaryotic cap-dependent translation pathway [1]. The myc family of genes when expressed are known to be involved in the control of cell growth, differentiation and apoptosis.
The Mnt internal ribosome entry site (IRES) is an RNA element. Mnt is a transcriptional repressor related to the Myc/Mad family of transcription factors. It is thought that this IRES allows efficient Mnt synthesis when cap-dependent translation initiation is reduced.
The N-myc internal ribosome entry site (IRES) is an RNA element found in the n-myc gene. The myc family of genes when expressed are known to be involved in the control of cell growth, differentiation and apoptosis. n-myc mRNA has an alternative method of translation via an internal ribosome entry site where ribosomes are recruited to the IRES located in the 5' UTR thus bypassing the typical eukaryotic cap-dependent translation pathway.
The HIF-1α internal ribosome entry site (IRES) is an RNA element present in the 5' UTR of the mRNA of HIF-1α that allows cap-independent translation. The HIF-1α internal ribosome entry site (IRES) allows translation to be maintained under hypoxic cell conditions that inhibit cap-dependent translation [1]. The hypoxia-inducible factor-1α protein (HIF-1α) is a subunit of the HIF-1 transcription factor, which induces transcription of several genes involved in the cellular response to hypoxia.
The Tobamovirus internal ribosome entry site (IRES) is an element that allows cap and end-independent translation of mRNA in the host cell. The IRES achieves this by mediating the internal initiation of translation by recruiting a ribosomal 43S pre-initiation complex directly to the initiation codon and eliminates the requirement for the eukaryotic initiation factor, eIF4F.
The TrkB internal ribosome entry site (IRES) is an RNA element which is present in the 5' UTR sequence of the mRNA. TrkB is a neurotrophin receptor which is essential for the development and maintenance of the nervous system. The internal ribosome entry site IRES element allows cap-independent translation of TrkB which may be needed for efficient translation in neuronal dendrites.
A ribosome binding site, or ribosomal binding site (RBS), is a sequence of nucleotides upstream of the start codon of an mRNA transcript that is responsible for the recruitment of a ribosome during the initiation of translation. Mostly, RBS refers to bacterial sequences, although internal ribosome entry sites (IRES) have been described in mRNAs of eukaryotic cells or viruses that infect eukaryotes. Ribosome recruitment in eukaryotes is generally mediated by the 5' cap present on eukaryotic mRNAs.
Eukaryotic translation initiation factor 4 G (eIF4G) is a protein involved in eukaryotic translation initiation and is a component of the eIF4F cap-binding complex. Orthologs of eIF4G have been studied in multiple species, including humans, yeast, and wheat. However, eIF4G is exclusively found in domain Eukarya, and not in domains Bacteria or Archaea, which do not have capped mRNA. As such, eIF4G structure and function may vary between species, although the human eIF4G 1 has been the focus of extensive studies.
