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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    30S Ribosomes engaged in translation initiation complex Figure 3.11 : Ribosome subunit cycle. When translation is terminated, the 70S ribosome, tRNA and a completed polypeptide chain separate. The ribosome joins a pool of 70S monomers. Ribosomes are withdrawn from the pool when they complex with a dissociation factor to give free 30S and 50S subunits. When a 30S subunit attaches to a messenger to form an initiation complex it releases its dissociation factor so that it can associate with a 50S subunit 70S ribosomes should lack the factor, whether they are engaged in protein synthesis or are free and awaiting dissociation. By using S 35 labelled f3, Sabol and Ochoa (1971) confirmed that the only particles in the cell which possess f3 are the free 30S subunits. Each 30S subunit appears to have one binding site for f3. When f3 is added to 70S ribosomes, they dissociate into subunits; figure 3.12 shows that the extent of dissociation is proportional to the amount of f3 added. When a 70S ribosome is generated by association of 30S and 50S sub- units (whether by formation of an initiation complex or by increasing the Mg 2+ concentration), the labelled f3 is released from the 30S subunit. The irrelevance of the reason for association of the subunits suggests that the release of 30S bound f 3 is a consequence of subunit association as such, perhaps