Protein factors involved in polypeptide chain initiation in Escherichia coli.

Abstract

The initiation of polypeptide chains synthesized from natural messenger RNA (mRNA) has been shown to proceed in cell-free bacterial systems with the incorporation of N-formyl-methionine (F-met) at the N-terminal positions (Adams and Capecchi, 1966; Webster et al., 1966). Two species of Met-tRNA have been found: Met-tRNAM, which recognizes an internal AUG codon and inserts methionine into a growing polypeptide chain, and Met-tRNAF, which is first formylated and then recognizes an AUG or GUG codon at the start of a cistron and initiates a new polypeptide chain (Clark and Marcker, 1966). A number of workers have reported that cell-free bacterial systems consisting of salt-washed ribosomes, GTP, and soluble factors are incapable of translating natural mRNA, while retaining full activity in Poly U-dependent polyphenylalanine synthesis (Eisenstadt and Brawerman, 1966; Revel and Gros, 1966; Stanley et al., 1966). Addition of ribosomal salt-wash restores activity toward natural mRNA, and has been shown to be...