Internal Ribosomal Structure

Figure 27.16 shows the shapes of the prokaryotic 70S ribosomes. The assembly of ribosomal subunits occurs in a specific order. Figure 27.19 shows interactions between proteins in the 30S subunit. Note the interactions between the proteins and that the order of addition of the proteins is critical. 30S and 50S subunits created by the kinds of in vitro reconstitutions are fully functional and can form 70S ribosomes:

30S + 50S <=> 70S

Formation of the 70S subunit is favored by increasing concentrations of magnesium. Dissociation of the 70S particle to the 30S and 50S subunits is favored by high concentrations of a monovalent cation, such as sodium or potassium. Under the ionic conditions in the cytosol, a substantial fraction of ribosomes are dissociated into free subunits.

See also: Initiation of Translation, Ribosomes

INTERNET LINK: Ribosome Database Project