Functional characterization of the eukaryotic SECIS elements which direct selenocysteine insertion at UGA codons

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Selenocysteine is the 21st amino acid, incorporated via a specific recoding mechanism at UGA codons.
• Selenoproteins play crucial roles in various biological processes, including antioxidant defense and thyroid hormone metabolism.
• The selenocysteine insertion sequence (SECIS) element is essential for this recoding process.

Purpose of the Study:

• To investigate the structural and functional requirements of SECIS elements for selenocysteine insertion.
• To determine the role of specific nucleotides within SECIS elements for their activity.
• To assess the flexibility of UGA codon positioning in selenoprotein synthesis.

Main Methods:

• Identification and characterization of SECIS elements in rat selenoprotein P mRNA.
• Site-directed mutational analysis of conserved nucleotides in SECIS elements.
• Functional assays to assess stop codon suppression at out-of-context UGA codons.

Main Results:

• Two functional SECIS elements were identified in the 3' UTR of rat selenoprotein P mRNA.
• Conserved nucleotides in the loop and stem regions of SECIS elements are critical for function.
• SECIS elements from different selenoprotein genes can suppress UGA codons, demonstrating flexibility.

Conclusions:

• Multiple contact sites within SECIS elements are required for efficient selenocysteine insertion.
• The presence of SECIS elements in selenoprotein mRNAs provides complete flexibility in the UGA codon's position.
• This flexibility is crucial for the diverse structures and functions of eukaryotic selenoproteins.