Physical localisation and cloning of the structural gene for E. coli initiation factor IF3 from a group of genes concerned with translation.

The structural genes for translational initiation factor IF3, threonyl-tRNA synthetase (TRS), the two subunits of phenylalanyl-tRNA synthetase (PRS), and a 12 000 mol. wt. protein of unidentified function are carried by the lambda p2 transducing phage. The localization of these genes on a restriction map of the Escherichia coli DNA insert was achieved by deletion mapping. In addition a set of plasmids carrying fragments of the original phage was constructed and helped to confirm these assignments. One plasmid, containing a 3.3 kb PstI fragment inserted into pBR322, does not code for any of the synthetase genes but causes strains carrying it to overproduce IF3.