A search for structurally similar cellular internal ribosome entry sites

Area of Science:

• Molecular Biology
• Genetics
• Virology

Background:

• Internal ribosome entry sites (IRES) mediate cap-independent mRNA translation, crucial for viral RNA and cellular under stress.
• Viral IRES share structure/function despite sequence divergence; cellular IRES lack conserved structures.
• The X-linked inhibitor of apoptosis protein (XIAP) IRES structure serves as a template for identifying novel cellular IRES.

Purpose of the Study:

• To conduct a genome-wide search for human 5'UTRs with structural similarity to the XIAP IRES.
• To identify novel cellular IRES with conserved function.
• To elucidate the defining characteristics of cellular IRES.

Main Methods:

• Genome-wide search of human 5'UTRs using the XIAP IRES structure.
• Empirical derivation of the XIAP IRES structure.
• Functional validation of identified IRES candidates.

Main Results:

• Identified three novel IRES candidates: Aquaporin 4 (AQP4), ELG1, and NF-kappaB repressing factor (NRF).
• AQP4 and ELG1 IRES structures show limited similarity to XIAP IRES.
• Identified shared trans-acting factors binding to both XIAP and novel IRES.

Conclusions:

• Cellular IRES are likely defined by specific short motifs and trans-acting factors, not overall structural conservation.
• This contrasts with viral IRES, which exhibit greater structural similarity.
• The findings provide a new framework for understanding cellular IRES diversity and function.