Purification of 70S ribosomes.

Here we describe the further purification of prokaryotic ribosomal particles obtained after the centrifugation of a crude cell lysate through a sucrose cushion. In this final purification step, a fraction containing ribosomes, ribosomal subunits, and polysomes is centrifuged through a 7%-30% (w/w) linear sucrose gradient to isolate tight couple 70S ribosomes, as well as dissociated 30S and 50S subunits. The tight couples fraction, or translationally active ribosome fraction, is composed of intact vacant ribosomes that can be used in cell-free translation systems.