Integration of the multiple controls regulating the expression of the arginase gene CAR1 of Saccharomyces cerevisiae in response to differentnitrogen signals: role of Gln3p, ArgRp-Mcm1p, and Ume6p.

Expression of the catabolic gene encoding arginase in Saccharomyces cerevisiae, CAR1, is controlled by multiple nitrogen signals, such as the presence of the inducer, arginine, and the nature and amount of the nitrogen source. The present study has determined or confirmed the identity of the proteins involved in these different controls, as well as their targets in the CAR1 promoter. We show that Gln3p activates CAR1 expression through the GATAA sequences in the absence of an optimal nitrogen source, such as ammonia, glutamine or asparagine. Ume6p, which also controls the expression of early meiotic genes, represses CAR1 expression through a sequence called URS, as a function of nitrogen availability. Thus, the responses to the quality of the nitrogen source and to nitrogen starvation are achieved through different cis- and trans-regulatory elements. At least one of the multiple Rap1p and Abf1p binding sites is required for the basal transcription of the gene. The UAS(arg), containing the previously defined "arginine boxes" is the region that responds to the inducer through the action of the ArgRp-Mcm1p proteins, and its deletion alone significantly affects growth on arginine as sole nitrogen source. The functional UAS(arg) is about 60 nucleotides long, and contains two sequences homologous to the binding site for MADS-box proteins, to which ArgRIp and Mcm1p belong. No obvious palindromic sequence similar to the binding site of Gal4p, Ppr1p or Put3p is present in the UAS(arg), although ArgRIIp contains a Zn(II)2Cys6 motif. Interestingly, we have found that induction of CAR1 expression by arginine in the presence of an optimal nitrogen source is counteracted by Gln3p, independently of its action at the GATAA sequences.