Non-acylated tRNA binding on rat liver 60S subunits

The ability of rat liver ribosomes and subunits to form complexes with non-acylated tRNAs in the absence of mRNA has been studied using nitrocellulose membrane filtration technique. Binding to 60S subunits required the integrity of the pCpCpA end of the tRNA molecule and was not decreased when unpaired guanine had been modified using kethoxal. Scatchard plot analysis suggests that large subunits have two binding sites, whose affinity constant values, relatively high, vary according to the ionic composition of the medium. Thus, the affinity constant of the stronger site (about 3. 10⁹ M^?1) is from 7 to 21 times higher than that of the weaker. High Mg²⁺ and low K⁺ concentrations stabilized binding to both sites. tRNA is at least partly retained on the subunits by heat-labile bonds.