A genomic survey of nitrogen assimilation pathways in budding yeasts (sub-phylum Saccharomycotina).

Sequenced genomes of 149 species of budding yeast (including 62 species with draft genomes that currently lack gene annotations) were surveyed for the presence of 24 genes associated with the assimilation of amines, uracil, dihydropyrimidines, purines, uric acid, allantoin, and nitrate as nitrogen sources. Genes for the assimilation of primary amines were distributed broadly across the Saccharomycotina while choline assimilation appeared to be mostly restricted to the families Debaryomycetaceae, Metschnikowiaceae, and Pichiaceae. Conversely, the uracil catabolic pathway was completely absent in Debaryomycetaceae and Metschnikowiaceae but present in the majority of the remaining Saccharomycotina. The super-pathway for assimilation of purines, uric acid, and allantoin was present in the majority of surveyed species. Genes for the assimilation of nitrate were restricted to a minority of species in families Phaffomycetaceae, Pichiaceae, and Trichomonascaceae as well as some currently unassigned genera. This study also successfully identified yeast homologs of all six previously known eukaryotic genes involved in the biosynthesis of the molybdenum cofactor, which is required for the activity of the nitrogen assimilation-associated enzymes nitrate reductase and xanthine oxidoreductase. Analysis of 1,187 upstream intergenic regions identified three novel putative regulatory motifs for the assimilation of uracil, purines, and uric acid as well as a possible role for the MADS-box transcription factor Mcm1 in the regulation of amine assimilation genes.