The synthesis of polyphenylalanine on ribosomes to which erythromycin is bound.

Erythromycin binds to the large subunit of Escherichia coli ribosomes at a specific site that is very close to the amino acid of aminoacyl-tRNA bound into the peptidyltransferase center, and to the site to which puromycin is bound, the P and A sites, respectively, of the classical two-site model of ribosome function. Both erythromycin and puromycin affect fluorescence from fluorescent derivatives of aminoacyl-tRNAs, while both puromycin and aminoacyl-tRNAs affect fluorescence of fluorescent derivatives of erythromycylamine. The results demonstrate unequivocally that erythromycin, deacylated tRNA, a peptidyl-tRNA analogue and puromycin can be bound simultaneously to the same ribosome. Nascent peptides of more than a few amino acids in length block binding of erythromycin to the ribosomes but, unlike most other peptides, long polyphenylalanine chains can be synthesized on ribosomes to which erythromycin is bound. It is suggested that this refractory synthesis in the presence of erythromycin reflects the atypical physical and structural properties of polyphenylalanine.