Structural and functional accommodation of nucleotide variations at a conserved tRNA tertiary base pair

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• The U8:A14 tertiary base pair is vital for the L-shaped structure of transfer RNAs (tRNAs).
• This base pair is highly conserved but exhibits natural variations, raising questions about its adaptability.

Purpose of the Study:

• To investigate if all 16 permutations of the U8:A14 base pair can be accommodated by a single tRNA framework and the bacterial translational system.
• To determine the functional and structural consequences of U8:A14 variations in alanine tRNA.

Main Methods:

• Expression of wild-type and 15 U8:A14 variants of an alanine tRNA amber suppressor in Escherichia coli.
• Testing the ability of each variant to suppress an amber mutation.
• Structural analysis using chemical probes and lead-cleavage reactions.

Main Results:

• 12 out of 15 U8:A14 variants were functional suppressors (sup+), with the G8:G14 variant showing efficiency indistinguishable from the wild type.
• Structural analysis revealed distinct conformations for the wild-type and G8:G14 variants, despite similar function.
• Three variants (sup-) exhibited non-functionality, likely due to altered backbone structure impacting tRNA stability or interactions with translation factors.

Conclusions:

• The bacterial translational apparatus can structurally and functionally accommodate a wide range of U8:A14 variations in tRNAs.
• While some structural differences exist between functional variants (e.g., G8:G14), they do not impair protein synthesis.
• Non-functional variants disrupt tRNA structure, affecting cellular stability and interactions crucial for protein synthesis.