How mutations in tRNA distant from the anticodon affect the fidelity of decoding

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• The ribosome translates genetic code into proteins using transfer RNA (tRNA).
• Mutations within tRNA molecules can disrupt the accuracy of protein synthesis, leading to miscoding.
• The Hirsh suppressor, a mutated tRNA(Trp), is known to read through UGA stop codons.

Purpose of the Study:

• To elucidate the structural mechanisms by which tRNA mutations (G24A and A9C) cause miscoding during translation.
• To understand how these mutations affect tRNA-ribosome interactions and decoding fidelity.

Main Methods:

• X-ray crystallography was used to determine the 3.2-Å resolution structures of the 70S ribosome.
• Complexes included EF-Tu and various aminoacyl tRNAs (native tRNA(Trp), G24A tRNA(Trp), A9C tRNA(Trp)) bound to cognate (UGG) or near-cognate (UGA) codons.

Main Results:

• Crystal structures revealed how G24A and A9C mutations facilitate tRNA distortion for decoding at near-cognate codons.
• The A9C mutation increases tRNA flexibility, while the G24A mutation stabilizes tRNA distortion via an additional hydrogen bond.
• These structural changes promote the misreading of UGA codons by mutated tRNAs.

Conclusions:

• Specific tRNA mutations can alter tRNA conformation and flexibility to promote miscoding.
• The findings provide insights into the structural basis of decoding fidelity and the impact of tRNA mutations.
• Each native tRNA likely adopts a unique ribosomal conformation for accurate decoding.