Lrodriguez glycolysis 37 model for gal gene

Unformatted text preview: e. Galactose is transported into the cell by the product of GAL2 (permease) Galactose GAL2 where it is converted to an inducer (I) by the product of GAL3. The Gal3 GAL3 The Gal3 and Gal5 genes are not regulated by galactose but GAL3 acts as an Gal5 GAL3 inhibitor of Gal80. Gal80 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 36 Pathway of Galactose Utilization: 6 Key Genes GAL2 permease galactose external galactose internal α-galactosidase MEL1 -Gal-Glumelibiose GAL1 kinase GAL7 transferase Gal-1-P UDP-Glu GAL5 mutase Glu-1-P Glu-6-P UDP-Gal epimerase GAL10 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez glycolysis 37 Model for Gal Gene Regulations The model for GAL gene regulation in yeast is based on the following The GAL observations: (1) GAL genes are expressed in abundance when yeast cultures are GAL shifted from galactose-free to galactose-containing media. (2) Unlinked genes (GAL4 and GAL80) affect the expression of these GAL80 affect genes. GAL4 is expressed constitutively and activates transcription of the GAL1, 2, 7, 10 and MEL1 genes by binding the UAS enhancers. In GAL1 10 MEL1 this position, the carboxy-terminal end of GAL4 interacts with a TATA box binding factor (TBF). binding ). (3) The TBF interacts with RNAPII to stimulate transcription of the adjacent gene. GAL80 interacts with the C-terminus of GAL4 to prevent activation of the TBF/RNAPII complex. (4) When yeast cells are grown in the presence of glucose (or a combination of glucose and galactose), the catabolite repressor protein (CRP) iinteracts with the DNA binding domain of GAL4 to prevent its nteracts binding to the UAS. binding BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 38 Mutation Analysis Mutational analysis has shown that the Gal genes (Gal1, 2, 7, Mutational Gal Gal1, 10 and Mel1) are induced by galactose and not expressed 10 are induced constitutively. constitutively Regulation is accomplished through the action of two additional Regulation regulatory proteins, GAL4 and GAL80. Mutations in GAL4 GAL4 GAL80 Mutations (Gal4-) produce an uninducible phenotype. A Gal80- mutation produce Gal80 produces a constitutive phenotype. As shown in the following figure, the GAL4 protein has a stimulatory affect (shaded arrows) on Gal gene transcription. Gal GAL80 blocks (T-bar) the affect of GAL4. GAL80 is an GAL80 antagonist of GAL4. antagonist The action of GAL80 is blocked when bound by the galactose The sensor protein,GAL3 (making GAL3 an antagonist of GAL80). sensor GAL3 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 39 Components of the Gal Regulatory Circuit II GAL10 GAL7 GAL1 GAL2...
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