Three protein factors IF1, IF2 and IF3 are involved in the initiation of translation in prokaryotes. No clear function has been assigned to the smallest of these three factors, IF1. Therefore, to investigate the role of this protein in the initi-ation process inEscherichia coliwe have mutated the cor-responding gene infA. Because IF1 is essential for cell viability and no mutant selection has so far been described, the infA gene in a plasmid was mutated by site-directed mutagenesis in a strain with a chromosomalinfA + gene, followedbydeletionof thisinfA + this approach, the six arginine residues of IF1 were altered to leucine or aspartate
