Volume 1

Gene expression / Benjamin Lewin.

  • Lewin, Benjamin.
Date:
1974-1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression / Benjamin Lewin. Source: Wellcome Collection.

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    ribosomes incubated with AUGGU 30 (not shown to scale) in presence of all components needed for protein synthesis except factor G ; this allows binding of the first two aminoacyl-tRNAs, but no translocation. The first 15-16 nucleotides of the mRNA are protected, including a length of 11-12 uridine residues. U UuUUU u-ir AUGGU ii^ U ii-i2 ^ uV when factor G and GTP are added, translocation can take place—about half the ribosomes react—to give fmet-val-tRA in the P site; protection of mRNA then extends three nucleotides further, and a fragment of about 15 uridine residues is recovered AUGGUUUUUUn Uu AUGGUUUUUU+ U U UU AUG6U 14-15 U. 14-15 when GMP-PCP is used instead of GTP, translocation cannot take place and the ribosome continues to protect only the first 12 uridine residues AUGGUUUUUuy UUU A AUG6UUU UU UUU u u u AUGGU 11-12 U 11-12 i I I I I I i i i i i i 15 13 11 9 14 12 10 ribosome complexes are treated with ribonuclease to degrade unprotected uridines the mRNA is isolated and the 5' terminal AUGG sequence is removed with T1 ribonuclease number of uridine residues in protected fragments £ » Co s §■ •8 S- S g s - Figure 2.17: Translocation requires factor G and moves the ribosome three nucleotides. The ribosome protects a length of about 15 residues from the P site to the entry point of mRNA. Upper: pretranslocation complexes protect U u _ 12 . Centre: post-translocation complexes protect U 14 _i 5 . Lower: complexes unable to undertake translocation because GMP-PCP has replaced GTP protect the U n _ 12 length. The ribosome therefore moves three nucleotides for every translocation event and requires factor G and GTP for this action. Data of Thach and Thach (1971) OS vo