Analysis of the effect of transcription factor Gcr2p on the SUC2 gene expression


Thesis Type: Postgraduate

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

Approval Date: 2002

Thesis Language: Turkish

Student: İPEK SAVAŞÇIOĞLU

Supervisor: Sezai Türkel

Abstract:

SUC2 gene of the yeast Saccharomyces cerevisiae encodes invertase enzyme which hydrolyse sucrose and raffinose. SUC2 gene expression is regulated by glucose repression and derepression mechanisms. Nucleosomes bind to the promoter region of SUC2 gene in the presence of high glucose in the growth media. In addition to nuclesomes, the binding of Miglp, Tuplp and Ssn6p complex to the promoter region of SUC2 is required for the glucose repression. Apart from these transcription factors, hexokinase 2p (Hxk2p) is also required for the glucose repression of SUC2 promoter. In the presence of low glucose in the growth media, glucose repression is terminated and SUC2 promoter becomes derepressed. For derepression, nucleosomes are modified and dissociates or displaced from the SUC2 promoter. For nucleosome modification, the activities of Snf/Swi complex is required. But, derepression by itself is not enough for the high levels of transcription from the SUC2 promoter. Certain transcription factors are also required for the high levels of transcription form the SUC2 promoter. Gcrlp (Glycolysis regulation- 1) has been identified as one of the transcriptional regulator of the SUC2 gene. Gcrlp is required for the transcriptional activation of glycolytic genes together with Gcr2p and Raplp. Transcription factor Sgclp is also required for the Gcrlp function on certain promoters. In this study, the effects of Gcr2p, Raplp and Sgclp on the SUC2 gene expression was analysed using Suc2-lacZ gene fusion and by measuring invertase activities in the gcr2, rapl and sgcl mutant strains of S. cerevisiae. Results obtained in this study indicates that Gcr2p is essential for the high levels of derepression of SUC2 gene. It was shown that the transcription of Suc2-lacZ gene fusion reduced approximately 50-fold in the gcr2 mutant strain of S. cerevisiae. In addition, it was also shown that invertase activity of gcr2 mutant reduced 10-20 fold depending on the growth conditions. But, invertase activity reduced only two fold in sgcl mutant yeast strain and it is not affected from the rapl mutation.