Inhibition of peptide initiation on reticulocyte ribosomes by edeine.

Abstract

Edeine, a small basic peptide antibiotic, is shown to inhibit initiation of polyphenylalanine and globin peptides with little or no effect on peptide extension in cell-free systems derived from rabbit reticulocytes. Approximately a 1 to 1 molar ratio of edeine to ribosomes is sufficient for maximum inhibition of synthesis. In a poly(U)-directed system the antibiotic inhibits deacylated tRNAPhe binding into the donor ribosomal site and enzymatic or nonenzymatic binding of phenylalanyl-tRNA into the acceptor site. Resistance to edeine inhibition of polyphenylalanine synthesis or phenylalanyl-tRNA binding is produced by preliminary incubation of deacylated tRNA, poly(U), and ribosomes to form an initiation complex with deacylated tRNAPhe bound into the donor ribosomal site. Edeine blocks binding of phenylalanyl-tRNA or methionyl-tRNA to the smaller ribosomal subunit; however, it has a surprising stimulatory effect on methionyl-tRNA binding or methionylpuromycin formation with recombined ribosomal subunits. Globin synthesis in vitro on ribosomes isolated from whole cells previously incubated with NaF is partially inhibited by a high concentration of edeine while NaF completely inhibits synthesis. These “NaF ribosomes” carry tRNAfMet apparently in the form of an initiation complex accumulated during inhibition of peptide initiation by NaF. Edeine appears to inhibit peptide initiation at a point prior to the reaction inhibited by NaF. It is suggested that edeine inhibits peptide initiation by blocking a critical site on the 40 S ribosomal subunits, thus preventing functional integration of endogenous mRNA or Met-tRNAfMet into an initiation complex.