Further characterization of ribosome releasing factor and evidence that it prevents ribosomes from reading through a termination codon.

Ribosome releasing factor, an Escherichia coli protein known to release ribosomes from mRNA at the termination codon, was purified from both the ribosomal wash and the soluble fractions to electrophoretical homogeneity. These preparations had a molecular weight of 23,500 determined by gel electrophoresis, and they were immunologically indistinguishable. Translation of various mRNA was stimulated up to 3-fold upon addition of ribosome releasing factor. On the other hand, amino acid incorporation into proteins programmed by a mutant R17 RNA (an amber mutation at the seventh triplet of coat cistron) was inhibited by this factor. In this system, the major polypeptide formed in the absence of this factor had a molecular weight very close to the authentic R17 coat protein, suggesting that ribosomes may read through the amber codon in the absence of ribosome releasing factor.