Date of Award
Doctor of Philosophy (PhD)
Rosemary A. Stuart
Dale Noel, Gail Waring, Pinfen Yang
Yeast mitochondrial ribosomes are composed of an rRNA scaffold, encoded by the mitochondrial genome and many different proteins, which, with the exception of one, are encoded by nuclear genes. These ribosomal proteins are imported into the mitochondrial matrix following their synthesis in the cytosol, however, little is known about the subsequent events which result in an assembled, translationally-competent ribosome. Many of the mitochondrial ribosomal proteins bear homology to bacterial ancestors. In addition to the acquisition of mitochondrial targeting signals, a number of these nuclearly-encoded ribosomal proteins have acquired additional domains, often at their C-termini, which are termed "mitochondrial-specific domains". The function(s) of these domains is currently unknown and it is postulated that they may be involved in the process of ribosomal assembly or for ensuring the targeting of the ribosome to the mitochondrial inner membrane where they are translationally-active.
Mrp20 protein is a nuclearly-encoded component of the mitochondrial large ribosomal subunit and shares homology with bacterial ribosomal protein L23, a protein located at the exit site of the ribosomal polypeptide tunnel. Mrp20 contains a C-terminal mitochondrial-specific domain of unknown function. In this study, we demonstrate that the C-terminal mitochondrial-specific region of Mrp20 is important to support the assembly of active mitochondrial ribosomes. It is proposed that the proteins at the exit site such as Mrp20 and MrpL40 are important for the assembly of mitochondrial ribosomes. Furthermore, the data presented here indicates that in the absence of the C-terminal region of the Mrp20 protein, the process of assembly of the ribosome becomes stalled, and the accumulation of a novel ribosome intermediate complex is observed. The characterization of this novel intermediate, which furthers our understanding of the assembly process of ribosomes in mitochondria, is presented.