Fig. 3. Sucrose density gradient of crosslinked and non-crosslinked (control) ribosomes with high (10.5 mM, orange curve) and low magnesium ions (1 mM). Crosslinked ribosomes (XL) do not completely dissociate in a low magnesium sucrose gradient (blue curve). In the control sample, 70S ribosomes dissociate into 30S and 50S subunit particles in low magnesium as shown by the black curve.