Genetic Analysis: An Integrated Approach (3rd Edition)
3rd Edition
ISBN: 9780134605173
Author: Mark F. Sanders, John L. Bowman
Publisher: PEARSON
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Chapter 12, Problem 11P
Explain the circumstances under which attenuation of operon gene expression is advantageous to a bacterial organism. Would you expect attenuation to be found in a single
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The attenuation mechanism that helps block expression of the tryptophan operon requires all of the following, except
A) O MRNA transcript of the trp leader sequence
B) Oaribosome stalled at the stop codon of the trp leader transcript
C) O formation of an attenuator loop
D) O low intracellular levels of tryptophan
You have isolated different mutants (reg1 and reg2) causing constitutive expression of the emu operon (which has genes emu1 and emu2). One mutant contains a defect in a DNA-binding site, and the other has a loss-of-function defect in the gene encoding a protein that binds to the site
Say you don’t know which mutant has a defect in the site and which one has a mutation in the binding protein. To figure it out, you construct the two partial diploid strains (i and ii below), and you then assay the levels of the Emu1 and Emu2 proteins in these two strains.
F’ (reg1- reg2+ emu1- emu2+) / reg1+ reg2+ emu1+ emu2-
F’ (reg1+ reg2- emu1- emu2+) / reg1+ reg2+ emu1+ emu2-
What proteins do you predict will be expressed for strains i and ii if reg2 encodes the regulatory protein and reg1 is the regulatory site?
Tryptophan (Trp) attenuation is an extra mechanism of regulation of trp operon when trp level is too high. Attenuation causes premature transcription termination.
b) Predict what will happen if trp repressor lose its allosteric effect.
Chapter 12 Solutions
Genetic Analysis: An Integrated Approach (3rd Edition)
Ch. 12 - 12.1 Bacterial genomes frequently contain groups...Ch. 12 - Transcriptional regulation of operon gene...Ch. 12 - Why is it essential that bacterial cells be able...Ch. 12 - Identify similarities and differences between an...Ch. 12 - The transcription of -galactosidase and permease...Ch. 12 - 12.6 Is attenuation the product of an allosteric...Ch. 12 - The trpL region contains four repeated DNA...Ch. 12 - The CAP binding site in the lac promoter is the...Ch. 12 - What role does cAMP play in transcription of lac...Ch. 12 - How would a cap- mutation that produces an...
Ch. 12 - Explain the circumstances under which attenuation...Ch. 12 - Consider the transcription of genes of the...Ch. 12 - Describe the lytic and lysogenic life cycles of ...Ch. 12 - 12.14 Define antisense RNA, and describe how it...Ch. 12 - 12.15 Attenuation of trp operon transcription is...Ch. 12 - 12.16 In the lac operon, what are the likely...Ch. 12 - Identify which of the following lac operon haploid...Ch. 12 - Prob. 18PCh. 12 - 12.19 List possible genotypes for lac operon...Ch. 12 - Suppose each of the genotypes you listed in parts...Ch. 12 - 12.21 Four independent mutants (mutants A to D)...Ch. 12 - Suppose the lac operon partial diploid...Ch. 12 - What is a riboswitch? Describe the riboswitch...Ch. 12 - 12.24 A repressible operon system, like the trp...Ch. 12 - 12.25 What is the likely effect of each of the...Ch. 12 - 12.26 Suppose that base substitution mutations...Ch. 12 - 12.27 Two different mutations affect. Mutant...Ch. 12 - How would mutations that inactivate each of the...Ch. 12 - The bacterial insertion sequence IS 10 uses...Ch. 12 - For an E. coli strain with the lac operongenotype...Ch. 12 - 12.31 How could antisense RNA be used as an...Ch. 12 - 12.32 Section describes the function of tRNA...Ch. 12 - The following hypothetical genotypes have genes A,...Ch. 12 - 12.34 Northern blot analysis is performed on...Ch. 12 - Prob. 35PCh. 12 - Prob. 36PCh. 12 - 12.37 The electrophoresis gel shown in part (a) is...
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- Gene expression in bacteria is controlled by the operon model. a) Why is the operon model important? b) Why is the trp operon known as a repressible operon?arrow_forwardA bacterial operon is responsible for the production of the biosyntheticenzymes needed to make the hypothetical amino acidtisophane (tis). The operon is regulated by a separate gene, R.The deletion of R causes the loss of enzyme synthesis. In the wildtypecondition, when tis is present, no enzymes are made; in theabsence of tis, the enzymes are made. Mutations in the operatorgene (O-) result in repression regardless of the presence of tis. Isthe operon under positive or negative control? Propose a modelfor (a) repression of the genes in the presence of tis in wild-typecells and (b) the mutations.arrow_forwardDescribe what would happen to the lac operon in a low-lactose environment and in a high lactose environment. a) How will each of these environments affect gene expression? b) What would happen to the repressor in each case? c) How will each of these environments affect RNA polymerase?arrow_forward
- In the presence of tryptophan, and a mutation in the allosteric domain that abolishes tryptophan binding______. a) the active repressor cannot bind trp), so operon gene transription is attenuated b) the inactive repressor cannot bind trpO, so operon gene transcription occurs] c) the active repressor binds trpP, so operon gene trasncription is repressed, the inducer cannot bind trpO, so gene transcription occurs d) the repressor binds to the corepressor, and an operon gene transcription occursarrow_forwardThe lac operon in E. coli bacteria codes for proteins that break down (digest) the disaccharide lactose. Therefore, the lac operon is expressed at its highest levels when there is: A) glucose but no lactose B) lactose and glucose C) lactose but no glucose D) no glucose or lactosearrow_forwardWhat would happen to the regulation of the tryptophan operon in bacterial cells that express a mutant form of the tryptophan repressor that (1) cannot bind to DNA, (2) cannot bind tryptophan, or (3) binds to DNA even in the absence of tryptophan?arrow_forward
- A number of mutations affect the expression of the lac operon in E. coli. Consider each genotype below and complete the table using “+” to indicate that the gene is expressed, and “−” to indicate that gene is not expressed.arrow_forwardWhat experimental results would indicate that the mutation lacISlacIS is dominant to lacI+lacI+? In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a repressed state in the absence of lactose. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a constitutive state in the absence of the repressor. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in an activated state in the presence of lactose. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a repressed state in the absence of the repressor. In lacISlacIS/lacI+lacI+ partial diploids, the lac operon is in a repressed state in the presence of lactose.arrow_forwardThe streptolysin S toxin made by S. pyogenes is encoded by a 9-gene operon, sagABCDEFGHI. Thinking about what a 3-line diagram would look like for this operon, answer the following questions. Write numeric answers only. For example, if your answer is 6 promoters, write only 6. 1) How many promoters control the expression of these genes? 2) How many locations does RNA Polymerase bind to get full expression of these genes? 3) How many ribosome binding sites are needed for full protein expression? 4) How many start codons will be needed for full protein expression? 5) How many mRNA strands will be produced with full operon expression? 6) How many proteins will be produced with full protein expression? 1arrow_forward
- Examine the following theoretical operon (gen) in E. coli which contains structural genes (genC, genB, genA) that are involved in amino acid biosynthesis. The gen operon also includes the gene encoding for the regulator molecule within it. When the amino acid that this operon helps synthesize is present, it binds to the regulator forming a complex which can bind to the operator region. Assume that the regulator molecule only binds to the operator in the presence of the amino acid. Question 1 Promoter Operator genC genB gen operon Regulator genA Transcription occurs when: A. The amino acid is not bound to the regulator, causing the regulator to bind to the operator. B. The amino acid is bound to the regulator, causing the regulator to bind to the operator. C. The amino acid is not bound to the regulator, causing the regulator to fail to bind to the operator. D. The amino acid is bound to the regulator, causing the regulator to fail to bind to the operator. E. The operon is…arrow_forwardExamine the following theoretical operon (gen) in E. coli which contains structural genes (genC, genB, genA) that are involved in amino acid biosynthesis. The gen operon also includes the gene encoding for the regulator molecule within it. When the amino acid that this operon helps synthesize is present, it binds to the regulator forming a complex which can bind to the operator region. Assume that the regulator molecule only binds to the operator in the presence of the amino acid. Promoter || Operator genC genB gen operon Regulator genAarrow_forwardWhat is the phenotype of an E. coli strain with a mutation in the lac operator that allows the lac repressor to irreversibly bind the operator? Assume glucose is absent. 1S A) O Transcription of the operon is very high whether lactose is present or not. B) O Transcription of the operon is very low whether lactose is present or not. C) O Transcription of the operon is high in the presence of lactose, and low in its absence. D) O Transcription of the operon is low in the presence of lactose, and high in its absence.arrow_forward
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