The DUR1,2 gene from Saccharomyces cerevisiae has been isolated on recombinant plasmids along with all DNA between the DURI,2 and MET8 loci. DUR1,2 was found to encode a 5.7-kilobase transcript, which is consistent with our earlier suggestion that the DURi and DUR2 loci are two domains of a single multifunctional gene. Steady-state levels of the DUR1,2 transcript responded to induction and nitrogen catabolite repression in the same way as urea amidolyase activity. da)81 mutants (grown with inducer) contained barely detectable amounts of DURI,2 RNA, whereas dal80 mutants (grown without inducer) contained the same amount as a wild-type induced culture. These observations support our earlier hypothesis that DUR1,2 is transcriptionally regulated, with control being mediated by the DAL80 and DAL8I gene products. We cloned the DUR1,2_Oh mutation and found it to be a Ty insertion near sequences required for complementation of durl,2 mutations.The ROAM phenotype of the DUR1,2_Oh mutation is sharply different from that of cis-dominant, DUR80 mutations, which enhance DUR1,2 expression but do not affect the normal control pattern of the gene. There is evidence that DUR80 mutations may also be Ty insertions, which generate phenotypes that are different from those in DUR1,2-Oh mutations.An appreciation for the molecular mechanisms involved in control and integration of procaryotic metabolic pathways has been gained by studying regulons with widely differing physiological functions (28, 31). Similar information is now beginning to accumulate for eucaryotic systems (42). Nitrogen catabolic systems are particularly useful for such investigations, because most are subject to multiple layers of regulation. Genes encoding the allantoin-degradative system in Saccharomyces cerevisiae, for example, respond to both induction and nitrogen catabolite repression (15,25,38 its 3-min half-life after the addition of asparagine to the medium (12). In contrast, enzyme activity is not lost after the addition of a repressive nitrogen source, but continued enzyme synthesis ceases (12). The lack of enzyme induction does not result from inducer exclusion, because daI80 mutants, which do not require the presence of an inducer for enzyme production, are similarly devoid of allantoindegrading enzymes when grown in glucose-asparagine medium (8).Earlier kinetic studies are consistent with the hypothesis that both induction and nitrogen catabolite repression are exerted at gene expression (1-4, 16, 24-26