1. Ribosomal RNA Phillips Huang BMS 265

2. rRNA Nomenclature Named based on sedimentation rates, measured in Svedberg units (S) Larger sedimentation coefficients indicate faster sedimentation rates Larger rRNAs sediment faster

3. rRNA Discovery First discovered in the 1930s as part of the microsome by Albert Claude Characterized as a ribosomal component in the 1950s by George Palade

4. Large Ribosomal Subunit rRNA largely responsible for 3D structure Peptidyl transferase center (PTC) composed of rRNA A, P and E sites made up mainly of rRNA

5. Small Ribosomal Subunit Atomic structure published in 2000 Decoding center composed entirely of rRNA

6. rRNA Biogenesis in Eukaryotes In prokaryotes, rRNAs are also synthesized as one primary transcript

7. Mechanism of action: Translation initiation in Prokaryotes Translation initiation in eukaryotes involves binding of ribosomal components first to the mRNA 5’ cap

8. Mechanism of action: Translation elongation Residues of rRNA help to stabilize the mRNA:tRNA complex

9. Peptide Bond Formation Involves nucleophilic attack of α-amino group of aminoacyl-tRNA on carbonyl carbon of peptidyl- tRNA Hypothesized transition state Target carbonyl carbon is protected from hydrolysis prior to reaction

10. Mechanism of action: Translation termination

11. rRNA as a Tool Phylogenetic studies –rRNA sequences are highly conserved across species In vitro translation systems –Used when overexpressed protein is toxic, rapidly degraded or insoluble in cells lancelets hagfish lamprey gnathostome

12. Role in Human Disease Mutations in mitochondrial rRNA –Susceptibility to aminoglycoside-induced hearing loss Changes to rRNA in cytoplasmic ribosomes –Defective pseudouridylation and X-linked Dyskeratosis Congenita (X-DC)