Studies on the function of two adjacent N⁶, N⁶-dimethyladenosines near the 3′ end of 16 S ribosomal RNA of Escherichia coli. IV. The effect of the methylgroups on ribosomal subunit interaction

The effect of the presence or absence of the methylgroups of the $m26Am26a$ sequence near the 3′ end of 16S rRNA of Escherichia coli on the interaction of the ribosomal subunits has been studied, using wild-type (methylated) and mutant (unmethylated) ribosomes. Subunit exchange experiments and competitive association experiments show a strong preference of the 50S subunit for association with methylated 30S subunits. The results indicate that the equilibrium constant of the reaction 70S $←→$ 30S + 50S is dependent on the methylgroups; mutant 30S·50S couples are lesss table than wild-type 30S·50S couples. It is postulated that the methylgroups also stimulate the interaction betveen 30S subunits and initiation factor IF-3.