Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biochemistry

Supervisor

Brandl, Chris J.

Abstract

Mistranslation occurs when an mRNA sequence is improperly decoded. Mistranslation can destabilize the proteome thus having a detrimental impact on the cell. tRNA variants with altered charging or decoding capabilities can increase mistranslation. Four mistranslating tRNAs were evaluated in yeast cells for their effect on growth, heat shock response, genetic interactions and cell morphology. Three of the tRNAs mistranslate at similar frequency, allowing for direct comparison of different amino acid substitutions. Each variant had distinct phenotypic consequences. Two of the tRNAs cause the same type of amino acid substitution but to different extents. The tRNA with the higher mistranslation frequency had a greater impact on the cell. These results demonstrate that the nature of the amino acid substitution and the extent of mistranslation influence the phenotype arising from a mistranslating tRNA. As the human genome contains distinct patterns of potential mistranslating tRNAs, these findings have consequences with respect to disease.

Summary for Lay Audience

Proteins are the molecular machines that allow cells to function. The information required to produce a protein is encoded in DNA. This information is converted into a protein through the processes of transcription and translation. During transcription, the information from DNA is copied into mRNA. During translation, the mRNA is decoded into a sequence of amino acids, the building blocks of proteins. Once the amino acid sequence is assembled, it is folded into the correct form to produce a functional protein.

The genetic code dictates how mRNAs are decoded into amino acids. Each mRNA is decoded in sections that are three nucleotides long. Each three-nucleotide sequence combination, otherwise known as codons, are assigned to one of the twenty amino acids or one of three stop signals. Mistakes can occur during this decoding process. When a codon is decoded as the wrong amino acid, it is known as mistranslation. These mistakes can change the structure of a protein causing it to become non-functional. A build-up of non-functional proteins can be toxic to the cell.

Transfer RNAs (tRNA) are key to the decoding process; they physically link an amino acid to its partner codon. At one end of the tRNA is a site that attaches to an amino acid; the other end of the tRNA pairs with a codon on the mRNA. Mutations that occur in tRNA genes can increase the likelihood of mistranslation. My studies centre on tRNA variants that cause mistranslation in yeast. I show that different mistranslating tRNAs have different effects depending on which amino acids are affected and how much mistranslation is caused. The study has implications for human health as variants of many tRNA genes exist in the human genome, some with the potential to cause mistranslation. I hypothesize that these variants effect the severity or age of onset of a number of diseases. My results imply that each of these variants may affect health and disease differently.

Available for download on Wednesday, March 31, 2021

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Biochemistry Commons

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