DIHYDROOROTATE (DHO(UT)) AND OROTATE (ORO(UT)) UTILIZER MUTANTS IN YEAST - IDENTIFICATION OF THE DHO(UT) MUTATION AND ALLELISM OF THE DHO AND URE2 GENES

We induced by UV mutagenesis a series of yeast mutants that were able to utilize dihydroorotic (dho(ut)) and erotic acid (oro(ut)) as precur sors for pyrimidine biosynthesis. These recessive mutations defined th ree complementation groups named dho(ut), oro(ut)1 and oro(ut)2. The w ild-type allele of the gene responsible for dihydroorotate utilization was cloned using the sensitivity of the dho(ut) mutant to 5-fluorooro tate. The DHO gene was sequenced and found to be identical to the URE2 gene. The dho(ut) mutation resulted from the introduction of a stop c odon instead of a glutamine at position 59, which led to the productio n of a truncated Ure2p. Therefore, the URE2 and DHO genes are alleles in yeast. ((C) Academie des sciences/Elsevier, Paris.)