Ribosomal RNA

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Ribosomal RNA

• Phillips Huang
• BMS 265

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rRNA Nomenclature

• Named based on sedimentation rates, measured in
  Svedberg units (S)
• Larger sedimentation coefficients indicate faster
  sedimentation rates
• Larger rRNAs sediment faster

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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

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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

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Small Ribosomal Subunit

• Atomic structure published in 2000
• Decoding center composed entirely of rRNA

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rRNA Biogenesis in Eukaryotes

• In prokaryotes, rRNAs are also synthesized as one
  primary transcript

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Mechanism of actionTranslation initiation in
Prokaryotes

• Translation initiation in eukaryotes involves
  binding of ribosomal components first to the mRNA
  5 cap

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Mechanism of actionTranslation elongation
Residues of rRNA help to stabilize the mRNAtRNA
complex
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Peptide Bond Formation

• Involves nucleophilic attack of a-amino group of
  aminoacyl-tRNA on carbonyl carbon of peptidyl-tRNA

Target carbonyl carbon is protected from
hydrolysis prior to reaction
Hypothesized transition state
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Mechanism of actionTranslation termination
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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

hagfish
gnathostome
lancelets
lamprey
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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)

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