Identification of the orotidine-5 '-phosphate decarboxylase gene and development of a transformation system in the yeast Saccharomyces exiguus Yp74L-3

To investigate the uracil biosynthetic pathway of the yeast Saccharomyces e xiguus Yp74L-3, uracil auxotrophic mutants were isolated. Using conventiona l genetic techniques, four mutant genes concerned in uracil biosynthesis we re identified and denoted as ura1, ura2, ura3, and ura4. Mutations in the U RA3 and URA4 genes were specifically selected with 5-fluoroorotic acid (5-F OA). Vector plasmids containing the URA3 gene and an autonomously replicati ng sequence (ARS) of S. cerevisiae produced sufficient amounts of Ura(+) tr ansformants from the ura4 mutant of S. exiguus. This fact indicates that th e S. exiguus URA4 gene encodes orotidine-5'-phosphate decarboxylase (OMP de carboxylase) and demonstrates that vector plasmids for S. cerevisiae are al so usable in S. exiguus.