CARBON AND NITROGEN-SOURCES REGULATE DELTA-AMINOLEVULINIC-ACID AND GAMMA-AMINOBUTYRIC-ACID TRANSPORT IN SACCHAROMYCES-CEREVISIAE

Evidence has been obtained showing that transport of delta-aminolevuli nic acid (ALA), a precursor of porphyrin biosynthesis in Saccharomyces cerevisiae, is mediated by the gamma-aminobutyric acid (GABA)-specifi c permease, UGA4. In yeast GABA is also incorporated by the general am ino acid permease (GAP1) and the specific proline permease (PUT4), The aim of the present work was to carry out a comparative study on the r egulation of ALA and GABA transport to confirm our proposal that both compounds share the UGA4 permease, ALA and GABA uptake, were measured in cells grown on minimal media with different carbon and/or nitrogen sources, To study the effect of the carbon source on UGA4 permease, AL A and GABA incorporation were measured in D27 strain, lacking GAP1 per mease, and grown in proline as the sole nitrogen source, so the activi ty of PUT4 permease was negligible, The effect of the nitrogen source on UGA4 permease was studied measuring ALA and GABA uptake rates in ce lls from media with ammonium, proline and urea as nitrogen sources, It was found that the regulation by the carbon source was similar on ALA and GABA transport; they depend equally on the energetic conditions o f the cells, Moreover, regulation by the nitrogen source on ALA and GA BA uptake was also similar, and identical to that described already fo r UGA4 permease. These results are further evidence that both compound s, ALA and GABA, share the GABA-specific permease, UGA4. (C) 1997 Else vier Science Ltd.