Ure2 internal ribosome entry site (IRES)

The Ure2 internal ribosome entry site (IRES) is a cis-acting RNA element found in the 5' untranslated region (5' UTR) of the URE2 mRNA in the yeast Saccharomyces cerevisiae. Unlike the canonical cap-dependent translation initiation mechanism, an IRES allows ribosomes to directly bind to mRNA internally, bypassing the need for a 5' cap structure for translation initiation. This cap-independent translation is particularly important under stress conditions, when cap-dependent translation may be inhibited.

The Ure2 IRES facilitates the translation of the Ure2 protein, which is involved in nitrogen regulation. Ure2 functions as a repressor of genes required for the uptake and metabolism of poor nitrogen sources. Under nitrogen-rich conditions, Ure2 represses the expression of these genes. However, under nitrogen-limiting conditions, Ure2 is inactivated, allowing the expression of genes required for the utilization of alternative nitrogen sources.

The structure and precise mechanism of action of the Ure2 IRES are not fully elucidated. However, it is known that the Ure2 IRES requires specific RNA secondary and tertiary structures for its function. These structures are thought to interact with ribosomal subunits and initiation factors to promote ribosome binding and translation initiation. The Ure2 IRES is a valuable tool for studying cap-independent translation and understanding the regulation of gene expression in response to environmental cues. Furthermore, IRES elements, including Ure2 IRES, have potential applications in biotechnology, such as in the design of vectors for efficient protein expression.