Nucleotide sequence of Escherichia coli pabB indicates a common evolutionary origin of p-aminobenzoate synthetase and anthranilate synthetase

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Abstract
Biochemical and immunological experiments have suggested that the E. coli enzyme p-aminobenzoate synthetase and anthranilate synthetase are structurally related. Both enzymes are composed of 2 nonidentical subunits. Anthranilate synthetase is composed of proteins encoded by the genes trp(G)D and trpE. p-Aminobenzoate synthetase is composed of proteins encoded by pabA and pabB. These 2 enzymes catalyze similar reactions and produce similar products. The nucleotide sequences of pabA and trp(G)D were previously determined and indicate a common evolutionary origin of these 2 genes. In this study, the nucleotide sequence of pabB was determined and compared with that of trpE. Similarities were 26% at the amino acid level and 40% at the nucleotide level. pabB an trpE may share a common ancestor, indicating that there is a common ancestry of genes encoding p-aminobenzoate synthetase and anthranilate synthetase.