Date of Award

2012

Degree Type

Dissertation

Department

Biological, Geological and Environmental Sciences

First Advisor

Mazumder, Barsanjit

Subject Headings

Ribosomes, RNA, L13a, ribosome biogenesis, rRNA methylation

Abstract

Ribosome biogenesis, a fundamental process, occurs in the nucleolus. It involves incorporation and association of ribosomal proteins (r-proteins) in the ribosomal subunit. Despite its obligatory and critical role in cellular function, the explicit mechanism of incorporation of different r-proteins into the pre-ribosome is not well understood. Using mammalian cell and r-protein L13a as our model, this study addresses the function and mechanism of r-protein incorporation during ribosome maturation. Published results from our laboratory showed the requirement of the release of L13a from the 60S ribosome to silence a cohort of inflammatory proteins directly at the level of translation thus showing the significant potential of this mechanism to resolve inflammation. To get further insight into the mechanism of its release, it is essential to identify the domain of L13a and the subcellular site required for ribosome incorporation. Homology modeling of human L13a with the crystal structure of prokaryotic L13, predicted some amino acid residues that could bind to ribosomal RNA (rRNA). Consistent with this model, a combined experimental approach involving ribosome incorporation assay of recombinant L13a and RNA immunoprecipitation have identified Arg at position 68 and Arg-Lys-Arg at position 59-60-61 as potential interaction site with 60S subunit. We have performed immunofluorescence studies to test whether the incorporation defective mutant L13a failed to translocate to the nucleolus, the site of ribosome biogenesis. L13a harboring the mutation of Arg at position 68 to Ala translocate to the nucleolus, but however alters the nucleolar morphology. In contrast L13a with the mutation of Arg-Lys-Arg at position 59-60-61 to Ala-Ala-Ala is nucleolar translocation incompetent. These studies also identified that incorporation of L13a during ribosome biogenesis occurs at the stage of 90S pre-ribosome formation. Previous studies from our laboratory showed an essential role of L13a in rRNA methylation. In these studies we identif

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