FIGURE 7.

Enhanced IF3 requirement for 70S ribosomes dissociation at low temperature. (A) Effect of increasing amounts of IF3 on the dissociation of 70S ribosomes at 37°C (□) and 15°C (■) in the presence of an IF1/ribosome ratio=1.5. Dissociation was quantitatively measured by sucrose density gradient centrifugation of “hybrid” 70S ribosomes constituted by nonlabeled 50S and [³⁵S]-labeled 30S as previously described (Petrelli et al. 2001). The dotted lines indicate the approximate amounts of IF3 required to obtain the dissociation of 50% of the 70S monomers at the two temperatures. Further details are given in Materials and Methods. (B) Schematic representation of the proposed role of IF3 in maintaining a sufficiently large pool of nonassociated 30S and 50S subunits during growth under optimal conditions of temperature and following the cold stress. See the text for explanations.