IRESs

Internal Ribosome Entry Sites, or IRESs, are nucleotide sequences within messenger RNA (mRNA) molecules that allow translation initiation in a cap-independent manner. Normally, translation in eukaryotes begins at the 5' cap of the mRNA. However, IRESs provide an alternative binding site for ribosomes downstream from the 5' end, enabling the ribosome to scan the mRNA and initiate translation at a specific internal start codon.

These sequences are found in a variety of eukaryotic mRNAs, including those encoding viral proteins, cellular proteins involved in stress responses, and in some bicistronic or multicistronic mRNAs where multiple proteins are translated from a single mRNA transcript. The structure and mechanism of IRESs are diverse, but they generally fold into complex secondary structures that recruit the ribosome and initiate translation.

The discovery of IRESs has significantly impacted our understanding of gene expression regulation. They play crucial roles in cellular processes such as stress response, apoptosis, and viral replication. Furthermore, IRES technology has been exploited in biotechnology for applications like the expression of multiple genes from a single transcript in gene therapy and the development of bi-cistronic vectors for protein production. Research continues to explore the full spectrum of IRES function and their potential applications.