We describe a Saccharomyces cerevisiae mutant affected in its urea and proline transport capacities, and a gene coding for a protein complementing this mutation. This protein is not membrane-embedded and contains two PEST sequences, often found in regulatory factors. The mRNA is not down-regulated under nitrogen catabolite repression, and is induced by urea and proline. In the mutant, the PUT4 mRNA encoding the proline permease is not affected, whereas the DUR3 mRNA, involved in urea active transport, is strongly increased. Our data suggest that this protein is a post-transcriptional regulator of nitrogen permeases.
