Biochemical and immnunological experiments have suggested that the Escherichia coli ,enzyme p,7amiilobenzoate synthetase and anthranilate synthetase are structurally related. Both enzymes are composed of two nonidentical subunits. Anthranliate synthetase is composed of proteins encoded by the genes trp(G)D and trpE, whereas p-aminobenzoate synthetase is composed of proteins encoded by pabA and pabB. These two enzymes catalyze similar reactions atd produce similar products. The nucleotide

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... es of pabA and trp(G)D have been determined and indicate a common evolutionary origin of these two genes. Here we present the nucleotide sequence ofpabB and compare it with that of trpE. Similarities are 26% at the amino acid level and 40% at the nucleotide level. We propose that pabB and trpE arose from a common ancestor and hence that there is a common ancestry of genes encoding p-aminobenzoate synthetase and anthranilate synthetase.