L-myc internal ribosome entry site (IRES)

The L-myc internal ribosome entry site (IRES) is a specific RNA element found within the 5' untranslated region (5' UTR) of the L-myc mRNA. Unlike the canonical cap-dependent translation initiation mechanism, which relies on the ribosome scanning from the 5' end of the mRNA, the L-myc IRES allows for cap-independent translation initiation. This means that the ribosome can directly bind to the mRNA at a specific internal site, bypassing the need for the 5' cap structure and associated initiation factors required for scanning.

The L-myc IRES is particularly important in situations where cap-dependent translation is compromised, such as during cellular stress, viral infection, or in specific cellular contexts where L-myc expression is critical. The presence and activity of the IRES can allow for continued translation of L-myc even when global cap-dependent translation is reduced.

The structure and specific RNA sequence of the L-myc IRES element are essential for its function. The IRES folds into a complex secondary or tertiary structure that facilitates the recruitment of ribosomes and initiation factors directly to the initiation codon. This bypasses the necessity of ribosome scanning from the 5' end of the mRNA, allowing for translation initiation even in the absence of a functional 5' cap or when ribosome scanning is impaired.

The L-myc IRES, by mediating cap-independent translation, plays a significant role in the regulation of L-myc expression. L-myc is a proto-oncogene involved in cell growth, differentiation, and apoptosis. Dysregulation of L-myc expression, often through mechanisms involving the IRES, has been implicated in the development and progression of various cancers. Therefore, the L-myc IRES represents a crucial regulatory element in controlling L-myc protein levels and influencing its downstream cellular effects.