Genetics: From Genes to Genomes
6th Edition
ISBN: 9781259700903
Author: Leland Hartwell Dr., Michael L. Goldberg Professor Dr., Janice Fischer, Leroy Hood Dr.
Publisher: McGraw-Hill Education
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Textbook Question
Chapter 16, Problem 35P
The E.coli MalT protein is a positive regulator of several mal operons, which are induced in the presence of the sugar maltose. The gene that encodes MalT was identified in a screen for mutants causing constitutive expression of mal operons; the operons were transcribed even in the absence of maltose. The screen involved a lacZ
transcriptional fusion reporter gene in which the regulatory region of a maltose-inducible operon was fused to the coding sequences of lacZ.
a. Bacteria with a lacZ- mutation are transformed with the reporter gene and spread on petri plates containing the β-galactosidase substrate X-gal. What color would the colonies be if the plates also contained maltose? What if the plates had X-gal but no maltose? |
b. In the screen, scientists mutagenized the lacZ- bacteria before transforming them with the reporter gene, and then spread the transformed bacteria on plates with X-gal and no maltose. All of the colonies were white except for one colony that was blue. At this stage of the analysis, researchers could not establish whether the gene mutant in the blue colony encoded a positive or a negative regulator of mal operons. Suppose first that the gene encoded a positive regulator. (i) How could the wild-type protein respond to maltose? (ii) How would the mutation affect protein function? (iii) Describe the likely nature of the mutation in the gene at the molecular level. Now answer these same three questions for the hypothesis in which the gene encoded a negative regulator (a repressor) of mal operon expression. |
c. How do you think the scientists figured out that MalT was a positive regulator and not a repressor? (Hint: Recall Fig. 14.28. Think about what would happen in each case if the researchers attempted to identify the malT mutant using a plasmid library made from the genome of a wild-type strain versus a plasmid library made from the genome of the mutant strain.) |
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Maltose utilization in E. coli requires the proteins encoded by genes in three different operons. One operonincludes the genes malE, malF, and malG; the secondincludes malK and lamB; and the genes in the thirdoperon are malP and malQ. The MalT protein is apositive regulator that controls the expression of allthree operons; expression of the malT gene itself iscatabolite sensitive.a. What phenotype would you expect to result from aloss-of-function mutation in the malT gene?b. Do you expect the three maltose operons to containbinding sites for CRP (cAMP receptor protein)?Why or why not?In order to infect E. coli, bacteriophage λ binds to themaltose transport protein LamB (also known as the λreceptor protein) that is found in the outer membraneof the bacterial cell. The synthesis of LamB is induced by maltose in the medium via expression of theMalT protein, as described above.c. List the culture conditions under which wild-typeE. coli cells would be sensitive to infection bybacteriophage…
The E. coli MalT protein is a positive regulator ofseveral mal operons, which are induced in the presenceof the sugar maltose. The gene that encodes MalT wasidentified in a screen for mutants causing constitutiveexpression of mal operons; the operons were transcribedeven in the absence of maltose. The screen involved alacZ transcriptional fusion reporter gene in which theregulatory region of a maltose-inducible operon wasfused to the coding sequences of lacZ.a. Bacteria with a lacZ− mutation are transformedwith the reporter gene and spread on petri platescontaining the β-galactosidase substrate X-gal.What color would the colonies be if the plates alsocontained maltose? What if the plates had X-galbut no maltose?b. In the screen, scientists mutagenized the lacZ− bacteria before transforming them with the reportergene, and then spread the transformed bacteria onplates with X-gal and no maltose. All of the colonies were white except for one colony that wasblue. At this stage of the…
A theoretical operon (theo) in E. coli contains several structural genes encoding enzymes that are involved sequentially in the biosynthesis of an amino acid. Unlike the lac operon, in which the repressor gene is separate from the operon, the gene encoding the regulator molecule is contained within the theo operon. When the end product (the amino acid) is present, it combines with the regulator molecule, and this complex binds to the operator, repressing the operon. In the absence of the amino acid, the regulatory molecule fails to bind to the operator, and transcription proceeds. Characterize this operon, then consider the following mutations, as well as the situation in which the wild-type gene is present along with the mutantgene in partially diploid cells (F¿):(a) Mutation in the operator region.(b) Mutation in the promoter region.(c) Mutation in the regulator gene.In each case, will the operon be active or inactive in transcription, assuming that the mutation affects the…
Chapter 16 Solutions
Genetics: From Genes to Genomes
Ch. 16 - For each of the terms in the left column, choose...Ch. 16 - The following statement occurs early in this...Ch. 16 - One of the main lessons of this chapter is that...Ch. 16 - All mutations that abolish function of the Rho...Ch. 16 - The figure at the beginning of this chapter shows...Ch. 16 - The promoter of an operon is the site to which RNA...Ch. 16 - You are studying an operon containing three genes...Ch. 16 - You have isolated a protein that binds to DNA in...Ch. 16 - You have isolated two different mutants reg1 and...Ch. 16 - Bacteriophage , after infecting a cell, can...
Ch. 16 - Mutants were isolated in which the constitutive...Ch. 16 - Suppose you have six strains of E. coli. One is...Ch. 16 - The previous problem raises some interesting...Ch. 16 - For each of the E. coli strains containing the lac...Ch. 16 - For each of the following growth conditions, what...Ch. 16 - For each of the following mutant E. coli strains,...Ch. 16 - Maltose utilization in E. coli requires the...Ch. 16 - Seven E. coli mutants were isolated. The activity...Ch. 16 - Cells containing missense mutations in the crp...Ch. 16 - Six strains of E.coli mutants 16 that had one of...Ch. 16 - a. The original constitutive operator mutations in...Ch. 16 - In an effort to determine the location of an...Ch. 16 - Prob. 23PCh. 16 - The footprinting experiment described in Fig....Ch. 16 - Why is the trp attenuation mechanism unique to...Ch. 16 - a. How many ribosomes are required at a minimum...Ch. 16 - The following is a sequence of the leader region...Ch. 16 - For each of the E. coli strains that follow,...Ch. 16 - Prob. 29PCh. 16 - For each element in the list that follows,...Ch. 16 - Among the structurally simplest riboswitches are...Ch. 16 - Great variation exists in the mechanisms by which...Ch. 16 - Many genes whose expression is turned on by DNA...Ch. 16 - In 2005, Frederick Blattner and his colleagues...Ch. 16 - The E.coli MalT protein is a positive regulator of...Ch. 16 - Prob. 36PCh. 16 - Prob. 37PCh. 16 - Prob. 38PCh. 16 - Prob. 39PCh. 16 - Prob. 40PCh. 16 - Prob. 41PCh. 16 - The researchers who investigated bioluminescence...Ch. 16 - Prob. 43PCh. 16 - Quorum sensing controls the expression of...Ch. 16 - Scientists are currently screening a chemical...
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- To study the lac operon, you engineer a strain of E coli to have a lac operon in which the lac Z gene is replaced by the gene for green fluorescent protein (GFP). Expression of GFP generates a green color in the cells that can be easily quantitated with a fluorescence microscope. You test the activity of the operon in the absence of the inducer IPTG, the presence of the inducer IPTG and the presence of an antibiotic the completely inhibits RNA polymerase (i.e. no gene expression). You then use this system to test the effects of various mutation on the activity of the operon. Match the following mutations with the activity (A, B or C) you would expect to observe with the mutation. All experiments are done in the presence of IPTG unless otherwise stated.arrow_forwardAn E. coli cell acquires a mutation in the gene that encodes CAP. The mutation affects the DNA-binding domain of CAP and ablates the ability of CAP to bind to the CAP site. Under which condition will the genes of the lac operon be transcribed at high levels? Glucose absent, lactose absent Glucose absent, lactose present Glucose present, lactose absent Glucose present, lactose present Under any of these conditions, the lac operon will not be transcribed at high levelsarrow_forwardThe diagram below represents the tryptophan operon with the trp leader mRNA transcript enlarged to represent the AUG translation start codon, two consecutive tryptophan amino acid codons (UGGUGG), and 4 regions (1, 2, 3, and 4) that base pair to form different hairpin-loop structures in the MRNA leader region. Suppose a mutant bacteria has region 4 of the trp operon attenuator region mutated so that it cannot base pair normally. Would the bacteria grow in the absence of the amino acid tryptophan? (hint: in order for bacteria to grow in absence of tryptophan it should be able to synthesize its own tryptophan) Lead&r region trpE trpD trpC trpB trpA DNA 5' 3' Transcription trp leader sequence MRNA UGGUGG 1 (tryptophan codons) AUG UUUUUU No There is insutficient information to answer the question. O Yesarrow_forward
- Given the following mutant and conditions, predict the expression of the lacZ gene (no expression, basal level, activate level of expression). A mutant of E. coli has a mutation in the promoter of the lac operon that prevents RNA polymerase from binding. + glucose, - lactose + glucose, + lactose – glucose, + lactosearrow_forwardSupply the words “off" or “on" in the blanks below: In an inducible operon, transcription is normally and must be turned In a repressible operon, transcription is normally and must be turned Briefly describe the overall function of the structural genes in the lac operon. Briefly describe the overall function of the structural genes in the trp operon. For the following descriptions of the bacterial lac operon, determine if lactose is present (P) or absent (A). The repressor is bound to the operator. The repressor is inactive. RNA polymerase transcribes the structural genes. Allolactose is bound to the repressor For the following descriptions of the bacterial trp operon, determine if tryptophan levels are high (H) or low (L). The repressor is bound to the operator. The repressor is inactive. RNA polymerase transcribes the structural genes. Tryptophan is bound to the repressor.arrow_forwardThe map of the lac operon is shown below. Consider the following examples that include both haploids and partial diploids and explain in each scenario whether the repressor can bind and regulate expression and whether or not the lac operon is expressed. For partial diploids the plasmid is indicated by the F’. I+ O+ Z+ Y+ / F’ I+ O+ Z+ Y+ I- O+ Z+ Y+ / F’ I+ O+ Z+ Y+ I- O+ Z+ Y+ I+ Oc Z+ Y+arrow_forward
- The diagram below represents a hypothetical operon in the bacterium E. coli. The operon consists of two structural genes (A and B), which code for the enzymes “Aase" and "Base", respectively, and also includes P (promoter) and O (operator) regions as shown. A В When a certain compound (X) is added to the growth medium of E. coli, the separate enzymes "Aase" and "Base" are both synthesized at a 50-fold higher rate than in the absence of X. (X has a molecular weight of about 200.) Which of the following statements is true of the operon described above? The region of the A gene that codes for the carboxyl-terminal amino acid of “Aase" is near the left end of the A gene. The P region contains nucleotide sequences to which the RNA polymerase holoenzyme (including the o subunit) binds specifically but which the core enzyme does not recognize. The addition of X to the growth medium causes a repressor protein to bind tightly to the O region. The mRNA copied from this operon will be covalently…arrow_forwardYou have isolated two different mutants (reg1 and reg2) causing constitutive expression of the emu operon (emu1 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. Is the DNA-binding protein a positive or negative regulator of gene expression? Explain. To determine which mutant has a defect in the site and which one has a mutation in the binding protein, you decide to do an analysis using F′ plasmids. Assuming you can assay levels of the Emu1 and Emu2 proteins, what results do you predict for the two strains (i and ii; see descriptions below) if reg2 encodes the regulatory protein and reg1 is the regulatory site? Explain. F′ (reg1− reg2+ emu1− emu2+)/reg1+ reg2+ emu1+ emu2− F′ (reg1+ reg2− emu1− emu2+)/reg1+ reg2+ emu1+ emu2−arrow_forwardThe molecules indicated below can be used experimentally due to their roles in relation to the expression of the lac operon. Drag the listed molecules to their corresponding bin. Reset Help ONPG IPTG X-Gal allolactose Dragable beta-galactosidase cleaves this molecule to form a visible yellow product. beta-galactosidase cleaves this molecule which then dimerizes to form a visible blue product. This molecule induces the transcription of the lac operon by inactivating the lac repressor.arrow_forward
- The dlagram below represents the tryptophan operon with the trp leader MRNA transcript enlarged to represent the AUG transiation start codon, two consecutive tryptophan amino acld codons (UGGUGG), and 4 regions (1, 2, 3, and 4) that base pair to form different hairpin-loop structures in the MRNA leader region. What would happen in this MRNA leader region when cells encounter very low levels of tryptophan in Its environment? Leader region trpE trpD trpC trpB trpA DNA 5' 3' Transcription trp leader sequence mRNA UGGUGG (tryptophan codons) AUG UUUUUU 1 3 4. The translating ribosome would stall at the two tryptophan codons, causing the formation of a hairpin-loop botween regions 3 and 4 to promote transcription of the trp operon. The translating ribosome would stall at the two tryptophan codons causing formation of hairpin-loop between regions 2 and 3, which functions as an anti-lerminator of transcription The translating ribosome would stall at the two tryptophan codons causing formation…arrow_forward1) The logic of the Lac operon was deciphered by using bacterial lac-operon mutants. Crucial to the experiments was creation of partial diploid cells in which operon from a wild-type cell is introduced into the mutant cell [thus there are 2 copies of the operon], and its ability to restore repression is assessed. Three classes of mutants were found that affect expression of the lac operon. Two of these resulted in constitutive expression of the operon, and the other eliminated all expression, even in the presence of lactose. Use the information above to complete the following table indicating with a (Y) yes or (N= No) if enzymatic activity of B-Gal will be detected (protein made and functional). Assume there is no glucose. Remember: Promoter for operon controls ALL genes downstream of it, coding sequence of the genes themselves matter (so if transcription is occurring but structural gene is producing a non-functional protein there will be no activity detected) For the lac operon…arrow_forwardThe lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products. These mutations include: I - = produces a repressor protein that cannot bind to the operator region IS = produces a repressor protein that cannot be removed from the operator region OC = cannot bind a repressor protein Z - = produces a defective (non-functioning) β-galactosidase enzyme + = wild type Detail the functionality of the lac operon under the following genetic and cellular conditions. You do not need to consider the role of CAP in your analysis. Genes Repressed (yes/no) Constitutive (yes/no) I+ OC Z+ I+ O+ Z+ (Lactose present) I- O+ Z+arrow_forward
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