Abstract
The Saccharomyces cerevisiae UGA4 gene, which encodes the gamma-aminobutyric acid (GABA) and delta-aminolaevulinic acid (ALA) permease, is well known to be regulated by the nitrogen source. Its expression levels are low in the presence of a rich nitrogen source but are higher when a poor nitrogen source is used. In addition, GABA can induce UGA4 expression when cells are grown with proline but not when they are grown with ammonium. Although vast amounts of evidence have been gathered about UGA4 regulation by nitrogen, little is known about its regulation by the carbon source. Using glucose and acetate as rich and poor carbon source respectively, this work aimed to shed light on hitherto unclear aspects of the regulation of this gene. In poor nitrogen conditions, cells grown with acetate were found to have higher UGA4 basal expression levels than those grown with glucose, and did not show UGA4 induction in response to GABA. Analysis of the expression and subcellular localization of the transcription factors that regulate UGA4 as well as partial deletions and site-directed mutations of the UGA4 promoter region suggested that there are two parallel pathways that act in regulating this gene by the carbon source. Furthermore, the results demonstrate the existence of a new factor operating in UGA4 regulation.
Highlights
The yeast Saccharomyces cerevisiae is widely used as a model organism to study the function of mammalian proteins
When the carbon source was acetate, a gluconeogenic substrate, basal expression levels in cells grown in derepressed conditions were higher than those observed in cells from glucoseproline medium and there was no significant GABA induction
No differences between wild-type cells grown with glucose or acetate were observed in lacZ expression driven by a 59 deletion of the UGA4 promoter lacking both UASGATA and UASGABA elements (Fig. 5a, b, d)
Summary
The yeast Saccharomyces cerevisiae is widely used as a model organism to study the function of mammalian proteins. The expression of the UGA4 gene, which encodes the c-aminobutyric acid (GABA) and d-aminolaevulinic acid (ALA) permease in S. cerevisiae, depends on GABA induction and NCR (Andre et al, 1993; Bermudez Moretti et al, 1996) Induction of this permease requires at least two positive-acting proteins, the specific Uga3p factor and the pleiotropic Dal81p/Uga35p factor Gln3p, another GATA transcription factor, upregulates the expression of UGA4 in the presence of inducer by competing with Dal80p/Uga43p for binding to the UASGATA sequence (Coffman et al, 1997; Soussi-Boudekou et al, 1997). The outcome of this competition influences basal levels of transcription. The role of the other positive and negative GATA factors, Gat and Gzf respectively, in UGA4 regulation has been poorly studied
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
