Comparative studies on specific and nonspecific binding of transfer ribonucleic acid to ribosomes.

The binding of aminoacyl transfer ribonucleic acid @RNA) to ribosomes in the presence of corresponding messenger RNA (specific binding) is compared with that in the absence of messenger RNA (nonspecific binding). Specific binding is much more sensitive to tetracycline than nonspecific binding, and the former is similar to, but not identical with, the latter in its response to changes in Mg++ concentration. On the other hand, trypsin treatment of ribosomes abolishes both nonspecific and specific binding of aminoacyl-tRNA to the ribosomes in a parallel fashion, indicating that ribosomal proteins are involved in the binding of aminoacyltRNA in general. Aminoacyl-tRNA bound in the absence of messenger RNA can be partially, but not totally, chased from ribosomes by the addition of messenger RNA which does not contain the code word for the ammo acid. For this removal of aminoacyl-tRNA by unrelated messenger RNA, unbound, specific aminoacyl-tRNA coded for by the messenger must be present. Thus, the removal is an exchange reaction with the incoming specific aminoacyl-tRNA, and the addition of messenger alone in the absence of incoming specific aminoacyl-tRNA does not remove the nonspecifically bound aminoacyl-tRNA.