THE GENE ENCODING THE MAJOR PROLINE TRANSPORTER OF ASPERGILLUS-NIDULANS IS UP-REGULATED DURING CONIDIOSPORE GERMINATION AND IN RESPONSE TO PROLINE INDUCTION AND AMINO-ACID STARVATION

In Aspergillus nidulans a highly specific L-proline transporter is enc oded by the prnS gene which is tightly linked to all other genes invol ved in proline catabolism. In mycelia, the expression of the pm struct ural genes is finely co-regulated in response to proline induction and nitrogen/carbon catabolite repression. In this study we establish tha t prnS expression is also activated during germination of conidiospore s. This activation persists until the development of Gh-old mycelia an d it is independent of proline induction mediated by the pathway-speci fic prnA gene product. We then show that, in mycelia, prnS transcripti on is activated in response to proline or histidine starvation. This p rocess has two components: a prnA-dependent and a prnA-independent com ponent. A cis-acting element that conforms to the consensus target of the GCN4/CPC1 transcriptional activators mediating amino acid biosynth esis activation in other fungi is involved in the activation of prnS t ranscription in response to amino acid starvation. We also show that t he stimulation of prnB expression in germinating conidiospores is not due exclusively to transient internal amino acid starvation occurring during the transition from conidiospore to mycelium. This is the first report that an amino acid transporter gene is upregulated during deve lopment and in response to amino acid starvation and specific amino ac id induction.