Imagine the situation shown in Figure Q8-12. In cell I, a transient signal induc
ID: 57970 • Letter: I
Question
Imagine the situation shown in Figure Q8-12. In cell I, a transient signal induces the synthesis of protein A, which is a transcriptional activator that turns on many genes including its own. In cell II, a transient signal induces the synthesis of protein R, which is a transcriptional repressor that turn off many genes including its own. In which of these situations will the cell “remember” that the progenitor cell had experienced the transient signal? Explain your reasoning.
Note: Questions 8-21 to 8-24 use the following information and the data in Figure Q8-21. These questions may be used independently or as a group.
You are interested in understanding the gene regulation of Lkp1, a protein that is normally produced in liver and kidney cells in mice. Interestingly, you find that the LKP1 gene is not expressed in heart cells. You isolate the DNA upstream of the LKP1 gene, place it upstream of the gene for green fluorescent protein (GFP), and insert this entire piece of recombinant DNA into mice. You find GFP expressed in liver and kidney cells but not in heart cells, an expression pattern similar to the normal expression of the LKP1 gene. Further experiments demonstrate that there are three regions in the promoter, labeled A, B, and C in Figure Q8-21, that contribute to this expression pattern. Assume that a single and unique transcription factor binds each site such that protein X binds site A, protein Y binds site B, and protein Z binds site C. You want to determine which region is responsible for tissue-specific expression, and create mutations in the promoter to determine the function of each of these regions. In Figure Q8-21, if the site is missing, it is mutated such that it cannot bind its corresponding transcription factor.
Figure Q8-21
8-21 Which of the following proteins is likely to act as a gene repressor?
(a) factor X
(b) factor Y
(c) factor Z
(d) none of the above
8-22 Which of the following proteins are likely to act as gene activators?
(a) factors X and Y
(b) factors X and Z
(c) factors Y and Z
(d) factor X only
8-23 Experiment 1 in Figure Q8-21 is the positive control, demonstrating that the region of DNA upstream of the gene for GFP results in a pattern of expression that we normally find for the LKP1 gene. Experiment 2 shows what happens when the sites for binding factors X, Y, and Z are removed. Which experiment above demonstrates that factor X alone is sufficient for expression of LPK1 in the kidney?
(a) experiment 3
(b) experiment 5
(c) experiment 6
(d) experiment 7
8-24 In what tissue is factor Z normally present and bound to the DNA?
(a) kidney
(b) liver
(c) heart
(d) none of the above
(A) CELLI OFF transient 9nal turns on transcription of activator mRNA activator protein turns on its own gene activator (B) CELL I OFF transient turns on transcription of repressor mRNA gene repressor turns off its ownExplanation / Answer
The activation of protein R signals the activation of many genes. This induces the cell to differentiate and the events that led to differentiation are retained I the cellular memory. However, since there is repression in cell I, there is no chance of passing the information; the cells do not undergo any process for functional activation of genes. Hence, cell I only can remember the transient signal.
8.21 C. Factor Z is the gene represor. It represses the expression of the protein in heart.
8.22 A. Factors X and Y. Factor X activate expression in the liver, whereas factor Y activates expression in the kidney.
8.23 A. 3. The previous experiment (exp-2) shows that the absence of either of the factors leads to expression of the protein only in heart but not in the liver and kidney. In experiment 3, only factor A is present, and expression of the protein is observed both in kidney and heart.
8.24 C. Heart. Factor Z is a repressor and is normally found bound to DNA.