On the mechanism of messenger RNA binding by E. coli 70 S ribosomes

Abstract

Various aspects governing the interaction of 3H-poly U with E. coli ribosomes have been investigated with the use of a simple filtration technique. The binding of poly U to ribosomes was found to be temperature-dependent; i.e. the polynucleotide attaches most efficiently at a critical temperature consistent with its ordered-state to random-coil transition. Moreover, the interaction of poly U with ribosomes was shown to be magnesium-dependent at all temperatures examined, although the interaction was markedly stimulated by high magnesium concentrations (greater than 12 mM) at 0°. At 23° no increase in association of poly U with ribosomes was noted above 12 mM magnesium. Ribosome – poly U complexes exhibited reduced association, analogous to polynucleotide "melting" profiles, and yielded a Tm of 25° (the temperature at which the complex is half dissociated). The decreased association of poly U with ribosomes at elevated temperatures, in addition to other observed effects in the presence of the two protein perturbant solvents ethylene glycol and dimethyl sulfoxide, has led to the conclusion that hydrogen bonding probably plays a prominent role in the stabilization of the ribosome–mRNA complex.