DISPARATE SEQUENCE CHARACTERISTICS OF THE ERYSIPHE-GRAMINIS F-SP HORDEI GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE GENE

The Erysiphe graminis f.sp.. hordei (Egh) glyceraldehyde-3-phosphate d ehydrogenase (gpd) gene was isolated and characterized. It contains ty pical promoter elements and has three introns, one of which is positio ned in the 5' untranslated region of the gene. The deduced aminoacid s equence has 87% similarity to gpd genes from other Ascomycete fungi. T his is at the same level as previously estimated among these fungi. Co mparison at the DNA level reveal similarities of only around 70%, whic h is 10% lower than previously reported. In an evolutionary tree based on the sequences from 18 fungal gpd genes, Egh falls into the group o f Ascomycetes located at a basal position. The regulatory region of th e Egh gpd gene has no homology to corresponding sequences in other fil amentous Ascomycetes. Codon usage was determined for the four characte rized Egh genes (tub2, Egh7, Egh16 and gpd) and found to be similar fo r all four genes. The results of the codon-usage analysis suggest that Egh is more flexible than other fungi in the choice of nucleotides at the wobble position. Codon-usage preferences in Egh and barley genes indicate a level of difference which may be exploited to discriminate between fungal and plant genes in sequence mixtures. The Egh gpd promo ter appears to be superior to that of the Egh beta-tubulin gene (tub2) for driving the E. coli beta-glucuronidase (GUS) gene in transformati on experiments.