Pleiotropic control of five eucaryotic genes by multiple regulatory elements

We have previously shown that allophanate acts as an inducer for five structural genes whose products participate in the degradation of allantoin by Saccharomyces cerevisiae. This observation led us to hypothesize that these genes might be controlled in common and to test the hypothesis by searching for mutants unable to induce production of the allantoin-degrading enzymes. Such mutants have been found. These strains grew poorly when provided with any of the allantoin pathway intermediates, but used other nitrogen sources normally. The mutations carried in these strains were recessive to wild-type alleles and complemented mutations in all known loci associated with the allantoin pathway. The locus containing the most thoroughly studied mutation (dal81-1) was not fund to be tightly linked to any of the allantoin pathway structural genes. The low basal levels of allantoin pathway enzymes observed in Dal81- strains remained the same whether or not the inducer was present in the growth medium. However, the levels of enzyme increased moderately when mutants were grown on poor nitrogen sources. From these observations, we conclude that dal81 mutant strains possess a defect in the induction of enzyme synthesis; enzyme production due to relief of nitrogen catabolite repression, however, appears normal. The observed epistatic relationships of mutations in the DAL80 and DAL81 loci suggest that their products may possess a reasonable degree of functional independence.