Molecular analysis of the effects of osmotic stress on the glucose repression in sacharomyces cerevisiae


Thesis Type: Postgraduate

Institution Of The Thesis: Bursa Uludağ University, Fen Bilimleri Enstitüsü, Biyoloji , Turkey

Approval Date: 2003

Thesis Language: Turkish

Student: YELİZ YÜCEL

Supervisor: Sezai Türkel

Abstract:

SUC2 gene of the yeast Saccharomyces cerevisiae encodes invertase enzyme, which is required for the hydrolysis of sucrose and raffinose. Transcription of SUC2 gene is regulated with a complex set of transcription factors and chromatin modifying complexes. Transcription of SUC2 is repressed by Miglp, Hxk2p and nucleosomes in the presence of the high amounts of glucose in growth media Another transcriptional regulatory factor Gcrlp is also required for the regulated expression of SUC2 gene. When glucose is limiting or absent in the growth media, Miglp and Hxk2p complex dissociates from the SVC2 promoter. Nucleosomes are also modified and displaced from the SUC2 promoter by Snf/Swi complex and histone acetyl transferase complexes. After that SUC2 gene becomes activated and invertase enzyme is synthesized. In addition to glucose repression, it was recently shown that other physiological conditions like osmotic stress also has a negative effect on the transcription of SUC2 gene and invertase synthesis in S. cerevisiae. Results of our studies indicated that osmotic stress does not act through the High Osmolarity Glycerol (HOG) pathway on SUC2 gene expression. Our results also indicated that osmotic stress prevents the derepresion of SUC2 gene. Because, results of this study showed that once the SUC2 gene transcription is activated osmotic stress can not repress the transcription of SUC2 gene. Hence it is conceivable that osmotic stress acts on Snf/Swi or HAT complexes that are required for the nucleosome mobilization on SUC2 promoter.