Date of Award

2024

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Specialization

Cell and Molecular Biology

Department

Cell & Molecular Biology

First Advisor

Steven Gregory

Abstract

The ribosome is the large macromolecular machine responsible for protein synthesis, the final step of gene expression, in all cells. It is made up of ribosomal proteins (r-proteins) and ribosomal RNA (rRNA), and how these many components assemble into a functionally active particle is only poorly understood. In this thesis, I have used the extremely thermophilic bacterium Thermus thermophilus as a model system to study the role of a specific ribosomal protein, bS20, in 30S ribosomal subunit assembly. Results from these experiments suggest a potential role in ribosome function once assembly has occurred.

All ribosomes are composed of two subunits, and in bacteria these are the 30S and 50S subunits, which combine to make up the full 70S ribosome. The larger 50S subunit consists of 23 rRNA, 5S rRNA, and typically 33 r-proteins (the actual number varies among species); this larger subunit is re-sponsible for catalyzing peptide bond formation, the reaction linking amino acids together. The smaller 30S subunit consists of 16S rRNA and typically 21 r-proteins and is responsible for reading the genetic code as expressed by messenger RNA (mRNA). The interface between the two subunits contains three tRNAs that act as a bridge between the mRNA and growing amino acid chain.

While a great deal is known about the final structure of the ribosome and its function during protein synthesis, much less is known about how the ribosome assembles and the impact of assembly defects on protein synthesis. The broader goal of this project is to identify interactions that are critical for major 16S rRNA folding events that must occur during 30S ribosomal subunit assembly. To help bring some of these interactions to light, I have focused on ribosomal proteins and how they contribute to this process. I have chosen to compare two ribosomal proteins, uS17 and bS20, and the effects resulting from deletion of either of the genes encoding them. These proteins are located near one another in the 30S ribosomal subunit but are involved in distinct RNA-RNA interactions. In constructing and characterizing a mutant lacking bS20, I found that this protein is not essential for viability. However, the severe growth phenotype of the mutant suggests important structural or functional roles for this protein. An increase in sensitivity to the antibiotic streptomycin also suggests a defect in decoding accuracy, consistent with observations with other species. These results form the foundation for a more detailed analysis of the role of bS20 in ribosome assembly and protein synthesis.

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