Constitutive expression of the UGA4 gene in Saccharomyces cerevisiae depends on two positive-acting proteins, Uga3p and Uga35p

The first specific precursor of porphyrin biosynthesis is delta-aminolevuli nic acid. delta-Aminolevulinic acid enters Saccharomyces cerevisiae cells t hrough the gamma-aminobutyric acid specific permease Uga4p. It was describe d that this permease is inducible by gamma-aminobutyric acid and its regula tion involves several specific and pleiotropic transcriptional factors. How ever, some studies showed that under certain growth conditions the synthesi s of Uga4p was not dependent on the presence of gamma-aminobutyric acid. To study the effect of the trails-acting factors Uga43p, Uga3p. Uga35p, Ure2p and Gln3p on the expression of UGA4, we measured gamma-aminobutyric acid a nd delta-aminolevulinic acid uptake in yeast mutant cells, lacking one of t hese regulatory factors, grown under different conditions. Experiments anal yzing the UGA4 promoter using a fusion construction UGA4. : lacZ were also carried out. The results show that the constitutive expression of the UGA4 gene found in cells under certain growth conditions depends on the presence of Uga3p and Uga35p. In contrast, Gln3p and Ure2p do not seem to have any effect on this constitutive mechanism. (C) 2000 Federation of European Micr obiological Societies. Published by Elsevier Science B.V. All rights reserv ed.