Derivation of a structural model for the c-myc IRES

Area of Science:

• Molecular Biology
• RNA Structure
• Gene Regulation

Background:

• The c-myc gene is crucial for cell growth and is often dysregulated in cancer.
• Internal ribosome entry segments (IRES) mediate cap-independent translation initiation, playing a role in gene expression regulation.
• Understanding the c-myc IRES structure is key to deciphering its regulatory mechanisms.

Purpose of the Study:

• To determine the secondary structure model of the c-myc internal ribosome entry segment (IRES).
• To investigate the functional relevance of identified structural elements.
• To explore the implications of IRES structure on c-myc expression regulation.

Main Methods:

• Utilized chemical probing of c-myc IRES RNA to constrain structure prediction programs.
• Employed RNA structure modeling and prediction algorithms.
• Performed site-directed mutagenesis to test the functional significance of structural elements.

Main Results:

• Derived a secondary structure model for the c-myc IRES, revealing a modular organization into two domains linked by an unstructured region.
• Identified unique structural motifs, including a GNNRA apical loop and an overlapping double pseudoknot in Domain 1, and an AUUU loop in Domain 2.
• Located the ribosome binding site 16 nucleotides downstream of the pseudoknots.
• Demonstrated that specific structural elements repress c-myc IRES function, and mutations in these elements can affect c-myc expression.

Conclusions:

• The c-myc IRES possesses a modular structure with two essential domains.
• Structural elements within the IRES can act as repressors of its function.
• Alterations in the c-myc IRES structure have significant implications for the dysregulation of c-myc expression in diseases like cancer.