Eukaryotic selenocysteine tRNA has the 9/4 secondary structure

Area of Science:

• Molecular Biology
• RNA Structure
• Biochemistry

Background:

• Two models exist for eukaryotic selenocysteine (Sec) tRNA secondary structure: the experimentally supported 9/4 structure and a theoretically derived 7/5 structure.
• Previous studies established the 9/4 structure with specific stem lengths (9 bp acceptor, 4 bp T-stem) and a 7/5 structure with a T-stem bulge.

Purpose of the Study:

• To provide further experimental evidence supporting the 9/4 secondary structure model for eukaryotic selenocysteine (Sec) tRNA.
• To investigate the functional importance of specific tRNA(Sec) structural elements, including the anticodon stem, V-arm, and D-stem, for serylation and selenylation.

Main Methods:

• Construction and analysis of various tRNA(Sec) mutants with altered secondary structures.
• Assessing the activity of these mutants in serylation and selenylation assays.

Main Results:

• Mutants designed to exclusively form the 9/4 structure remained active for serylation and selenylation.
• Some mutants lacking the 6 bp anticodon stem, predicted essential by an alternative model, were still active.
• V-arm orientation and a rigid 6 bp D-stem were found to be important for selenylation activity.

Conclusions:

• The findings strongly support the 9/4 secondary structure model for eukaryotic and archaeal tRNA(Sec).
• All tRNA(Sec) molecules, regardless of domain (Eukarya, Archaea, Bacteria), share a conserved 13 bp domain II formed by stacked acceptor and T-stems.
• Specific structural features, like the D-stem and V-arm orientation, play critical roles in selenylation efficiency.