Q.12 A truncated polypeptide is synthesized due to a nonsense mutation. Where would you introduce
another mutation to obtain a full-length polypeptide?
(A) Ribosomal protein gene (B) Transfer RNA gene
(C) DNA repair gene (D) Ribosomal RNA gene
Nonsense mutations introduce premature stop codons, yielding truncated polypeptides during translation. Introducing a mutation in the transfer RNA (tRNA) gene enables suppressor tRNAs that recognize these stops as sense codons, restoring full-length protein synthesis. This strategy proves vital in genetic engineering and therapeutic applications.
Correct Answer
Option (B) Transfer RNA gene holds the solution. Suppressor tRNAs arise from anticodon mutations in tRNA genes, pairing with UAG, UAA, or UGA stops to insert amino acids and bypass termination. Techniques like CRISPR-pass enhance this readthrough, rescuing ~95% of clinically relevant nonsense mutations without DNA cleavage.
Option Analysis
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Ribosomal protein gene (A): Alters ribosomal structure or fidelity but fails to directly suppress specific stop codons; impacts global translation accuracy without targeted readthrough.
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Transfer RNA gene (B): Anticodon editing creates amber, ochre, or opal suppressors, allowing continued elongation at PTCs for functional full-length proteins in model systems.
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DNA repair gene (C): Affects genomic fidelity or mutation correction pre-transcription; does not influence translation of existing mutant mRNA transcripts.
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Ribosomal RNA gene (D): Mutations can modulate decoding center activity for general suppression but lack codon specificity compared to tRNA engineering.
Research Applications
In biotechnology, tRNA suppressors aid mammalian cell culture studies of disease proteins like CFTR or dystrophin, bypassing PTCs in patient fibroblasts. This kinase-independent method supports enzyme kinetics assays and genetic rescue, optimizing SEO-driven scientific workflows.
