The TRP1 gene of Phytophthora parasitica encoding indole-3-glycerolphosphate synthase-N-(5'-phosphoribosyl)anthranilate isomerase: structure and evolutionary distance from homologous fungal genes.

The TRP1 gene was isolated from the genome of Phytophthora parasitica. It encodes bifunctional enzyme of the tryptophan biosynthetic pathway indole-3-glycerolphosphate synthase-N-(5'-phosphoribosyl)anthranilate isomerase (IGPS-PRAI). The gene was localized and sequenced using random in vitro insertions of omega interposon. The domain structure of the protein product was found to be similar to that of enteric bacteria but different from the structure of homologous enzymes in fungi. Two introns in the IGPS domain were found. This is unique in eukaryotic IGPS-encoding genes so far sequenced. Comparative analysis of the primary structure of IGPS and PRAI domains [neighbor-joining method of Saitou and Nei, Mol. Biol. Evol. 44 (1987) 406-425] confirmed a large phylogenetic distance of TRP1 from corresponding fungal genes. In the resulting distance tree Phytophthora sequences are located outside of the cluster which encompasses all known homologous proteins from fungi indicating that the lineage of oomycetes took a separate course of development before speciation within the fungal line of descent began. Two of the oligopeptide insertions engineered into the F domain of the protein product did not abolish the enzymatic activity of the protein.