Transcriptional Regulation of GLT1 (GOGAT) in Saccharomyces cerevisiae

AVENDAÑO, A.; VALENZUELA, L.; GUZMÁN-LEÓN, S.; HERNÁNDEZ, C.; ARANDA, C.; GONZALEZ, A.

Rimini, Italy.

Congreso; XIX International Conference on Yeast Genetics and Molecular Biology; 1999

Federation of European Microbiological Societies

GOGAT (glutamate synthase) is one of the three enzymes whose function is the synthesis of glutamate in S. cerevisiae. GOGAT enzyme is codified by the GLT1 gene. We found that GLT1 expression is negatively regulated by glutamate, the product of the GOGAT enzyme reaction. GLT1 transcription is positively controled by Gln3p and Gcn4p, the general transcription factors from the NCR and GCN control systems (Valenzuela et al., 1998. J. Bacteriol. 180, 3533-3540). Deletion analysis of the promoter region suggested that a palindromic region and a nearby GATA box, were involved in GLT1 expression. Directed mutagenesis of the palindromic region showed that it acts positively in GLT1 expression, suggesting that a Cys6-Zn1 family factor is involved in GLT1 regulation. We are also conducting the site directed mutagenesis of the GATA box in order to know if both the palindromic and GATA cis elements are working together to sustain normal levels of GLT1 transcription. Experiments are under way to clone the factor that binds the palindromic region. In order to find another regulators of GLT1 expression we isolated a glutamate auxotroph from a gdh1-Iess strain. This mutant had reduced levels of GOGAT activity, which were recovered by complementation with GCN5 gene. We analyzed the expression of a GLT1-IacZ fusion in strains that were mutated in genes coding for members of the ADA/ GCN5 complex (ada2/ada3/gcn5) and found that both, GLT1 basal expression and GLT1 activated expression under aminoacid deprivation conditions, depended on a functional ADA/GCN5 complex. These results indicate that GLT1 gene expression is also determined by chromatin remodeling.