Date of Award
Summer 2007
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Stuart, Rosemary
Second Advisor
Noel, Dale
Third Advisor
Schlappi, Michael
Abstract
Oxa1 is a member of the conserved Oxa1/YidC/ Alb3 protein family involved in the translocation of membrane proteins. The yeast Saccharomyces cerevisiae mitochondrial Oxa1 protein is important for the biogenesis of a number of mitochondrial oxidative phosphorylation (OXPHOS) complexes, including the cytochrome bct, cytochrome oxidase (COX) and F1F0-ATP synthase complexes. A role for Oxa1 in facilitating the membrane insertion of mitochondrially encoded COX subunits 1, 2 and 3 (Cox 1, Cox2 and Cox3, respectively) has been previously identified. Oxa1 is required for the assembly of the COX complex. Oxa1 has been shown to interact with Cox 1, Cox2 and Cox3 during their synthesis as nascent chains and in a manner that is supported by mitochondrial ribosome. However, how Oxa1 comes in contact with these nascent chains and whether the ribosome interacts directly with Oxa1 has not been investigated in these earlier studies and is a focal point of the current study. The involvement of Oxa1 in the biogenesis of the COX complex has been studied in depth to date. However, the precise nature of Oxa1's involvement in the biogenesis of other OXPHOS complexes, such as the F1F0-ATP synthase has not been analyzed in detail. To gain insight into the mechanism of the Oxal-mediated membrane protein insertion, the first part of the current study is focused on the investigation of the possible interaction of Oxa1 with the mitochondrial ribosome. Nascent chains exit the ribosome through a tunnel-like structure in the large ribosomal subunit, known as the nascent polypeptide exit tunnel. The possible interaction of inner membrane protein Oxa1 with the large ribosomal subunit was therefore investigated. The close proximity of Oxa1 to ribosomal proteins which are localized close to the nascent chain exit site of the large ribosomal subunit was also tested. Furthermore, the importance of the conserved matrix-located Cterminal region of Oxa1 in facilitating the proposed interaction of Oxa1 with the ribosome and for the membrane insertion function of Oxa1 was investigated. The findings made through this part of the research led to the proposal that interaction of Oxa1 with ribosome serves to enhance a coupling of translation and membrane insertion events of newly synthesized proteins...