Structural Organization of the TRP1 Gene of Phycomyces Blakesleeanus: Implications for Evolutionary Gene Fusion in Fungi

The complete nucleotide (nt) sequence of the cloned TRP1 gene from Phycomyces blakesleeanus is reported. The gene encodes a trifunctional polypeptide that represents a sequential fusion of glutamine amidotransferase (TrpG), indoleglycerolphosphate synthetase (TrpC), and phosphoribosylanthranilate isomerase (TrpF) activities from the amino- to the carboxy terminus. This genetic organization is characteristic of filamentous fungi in general. The transcription start sites and the polyadenylation sites of the gene have been mapped. The two predominant TRP1 transcripts have a short leader of 13 and 18 nt, while minor species with significantly longer leaders are also detectable. Approximately 50 bp and 70 bp upstream from the major transcription start points, sequences that match the canonical eukaryotic TATA and CAAT boxes, respectively, are found. Two major polyadenylation signals are located approximately 50 and 70 nt downstream from the translational stop. Three closely clustered minor polyadenylation sites map to roughly 120-150 bp 3' to the termination codon. The TRP1 gene is the first and only Phycomyces gene that has been cloned and sequenced. The information regarding the promoter and terminator of a Phycomyces gene derived from these studies should benefit strategies aimed at gene manipulations in this organism.