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1. GAL4 is a specific transcription factor that activates the transcription of several genes in yeast. GAL80 inhibits GAL4's ability to activate (by binding to, and thereby masking, GAL4's activation site) unless galactose is available. How might galactose mediate this effect? One possibility is that galactose interacts directly with GAL80, changing its conformation and thereby changing the way it interacts with GAL4 (i.e. analogous to the conformational change induced in lac repressor when it binds inducer). However, there is strong evidence arguing against this possibility. There is genetic evidence that a gene called gal3 (which we will not discuss in class) influences the response of the GAL regulon to galactose. This question concerns the role of GAL3. The phenotypes associated with mutations in gal3 are shown in the table below. (Note that gal7 is one of the structural genes regulated by GAL4. Assume that the alleles described in this table are "null" alleles- that is, they are equivalent to deletion of the corresponding gene.)

1. GAL4 is a specific transcription factor that activates the transcription of several genes in yeast. GAL80 inhibits GAL4's ability to activate (by binding to, and thereby masking, GAL4's activation site) unless galactose is available. How might galactose mediate this effect? One possibility is that galactose interacts directly with GAL80, changing its conformation and thereby changing the way it interacts with GAL4 (i.e. analogous to the conformational change induced in lac repressor when it binds inducer). However, there is strong evidence arguing against this possibility. There is genetic evidence that a gene called gal3 (which we will not discuss in class) influences the response of the GAL regulon to galactose. This question concerns the role of GAL3. The phenotypes associated with mutations in gal3 are shown in the table below. (Note that gal7 is one of the structural genes regulated by GAL4. Assume that the alleles described in this table are "null" alleles- that is, they are equivalent to deletion of the corresponding gene.)

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
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Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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1. GAL4 is a specific transcription factor that activates the transcription of several genes in yeast. GAL80 inhibits GAL4's ability to activate (by binding to, and thereby masking, GAL4's activation site) unless galactose is available. How might galactose mediate this effect? One possibility is that galactose interacts directly with GAL80, changing its conformation and thereby changing the way it interacts with GAL4 (i.e. analogous to the conformational change induced in lac repressor when it binds inducer). However, there is strong evidence arguing against this possibility. There is genetic evidence that a gene called gal3 (which we will not discuss in class) influences the response of the GAL regulon to galactose. This question concerns the role of GAL3. The phenotypes associated with mutations in gal3 are shown in the table below. (Note that gal7 is one of the structural genes regulated by GAL4. Assume that the alleles described in this table are "null" alleles- that is, they are equivalent to deletion of the corresponding gene.) gal7 transcription -galactose wild-type gal4- gal80- gal3- gal3- gal80- low low high low high + galactose high low high low high (i) Draw out a regulatory scheme that is consistent with these results and that describes the regulatory interactions between GAL3, GAL4, and GAL80. Your scheme should be diagrammed using the symbols for activation and repression that we have used previously (e.g. A--> B ---I C--> structural genes.) Your scheme should end with GAL4 --> structural genes. (ii) Now, consider two more pieces of data: (1) A missense mutation in gal80 is discovered that causes GAL80 to inhibit GAL4 even in the presence of galactose. The gal structural genes are not induced by galactose in this strain. A second-site suppressor of this mutation is discovered that maps in gal3; this second mutation restores the galactose-inducibility of the gal structural genes. (The strain with both mutations is a "pseudo revertant"). (2) GAL3 is closely related to the enzyme galactokinase, which uses galactose as a substrate. However, it lacks galactokinase activity.
Transcribed Image Text:1. GAL4 is a specific transcription factor that activates the transcription of several genes in yeast. GAL80 inhibits GAL4's ability to activate (by binding to, and thereby masking, GAL4's activation site) unless galactose is available. How might galactose mediate this effect? One possibility is that galactose interacts directly with GAL80, changing its conformation and thereby changing the way it interacts with GAL4 (i.e. analogous to the conformational change induced in lac repressor when it binds inducer). However, there is strong evidence arguing against this possibility. There is genetic evidence that a gene called gal3 (which we will not discuss in class) influences the response of the GAL regulon to galactose. This question concerns the role of GAL3. The phenotypes associated with mutations in gal3 are shown in the table below. (Note that gal7 is one of the structural genes regulated by GAL4. Assume that the alleles described in this table are "null" alleles- that is, they are equivalent to deletion of the corresponding gene.) gal7 transcription -galactose wild-type gal4- gal80- gal3- gal3- gal80- low low high low high + galactose high low high low high (i) Draw out a regulatory scheme that is consistent with these results and that describes the regulatory interactions between GAL3, GAL4, and GAL80. Your scheme should be diagrammed using the symbols for activation and repression that we have used previously (e.g. A--> B ---I C--> structural genes.) Your scheme should end with GAL4 --> structural genes. (ii) Now, consider two more pieces of data: (1) A missense mutation in gal80 is discovered that causes GAL80 to inhibit GAL4 even in the presence of galactose. The gal structural genes are not induced by galactose in this strain. A second-site suppressor of this mutation is discovered that maps in gal3; this second mutation restores the galactose-inducibility of the gal structural genes. (The strain with both mutations is a "pseudo revertant"). (2) GAL3 is closely related to the enzyme galactokinase, which uses galactose as a substrate. However, it lacks galactokinase activity.
Propose a hypothesis for the molecular roles of GAL80, GAL3, and GAL4 in the regulation of the gal genes. Describe how your hypothesis accounts for each of the findings outlined above.
Transcribed Image Text:Propose a hypothesis for the molecular roles of GAL80, GAL3, and GAL4 in the regulation of the gal genes. Describe how your hypothesis accounts for each of the findings outlined above.
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