Genetics: From Genes to Genomes, 5th edition
5th Edition
ISBN: 9780073525310
Author: Leland H. Hartwell, Michael L. Goldberg, Janice A. Fischer, Leroy Hood, Charles F. Aquadro
Publisher: McGraw-Hill Education
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Chapter 15, Problem 10P
Mutants were isolated in which the constitutive
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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…
What 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.
. Mutants were isolated in which the constitutive phenotype of a missense lacI mutation was suppressed.That is, the operon was now inducible. These suppressor mutations mapped to the operon, not to the lacIgene. What could these mutations be?
Chapter 15 Solutions
Genetics: From Genes to Genomes, 5th edition
Ch. 15 - For each of the terms in the left column, choose...Ch. 15 - The following statement occurs early in this...Ch. 15 - One of the main lessons of this chapter is that...Ch. 15 - All mutations that abolish function of the Rho...Ch. 15 - The promoter of an operon is the site to which RNA...Ch. 15 - You are studying an operon containing three genes...Ch. 15 - Prob. 7PCh. 15 - You have isolated two different mutants reg1 and...Ch. 15 - Bacteriophage , after infecting a cell, can...Ch. 15 - Mutants were isolated in which the constitutive...
Ch. 15 - For each of the E. coli strains containing the lac...Ch. 15 - For each of the growth conditions listed, what...Ch. 15 - For each of the following mutant E. coli strains,...Ch. 15 - Maltose utilization in E. coli requires the...Ch. 15 - Seven E. coli mutants were isolated. The activity...Ch. 15 - Prob. 16PCh. 15 - Six strains of E.coli mutants 16 that had one of...Ch. 15 - a. The original constitutive operator mutations in...Ch. 15 - Prob. 19PCh. 15 - Figure 15.16 on p. 525 shows that in the lac...Ch. 15 - Why is the trp attenuation mechanism unique to...Ch. 15 - a. How many ribosomes are required at a minimum...Ch. 15 - The following is a sequence of the leader region...Ch. 15 - For each of the E. coli strains that follow,...Ch. 15 - One mechanism by which antisense RNAs act as...Ch. 15 - For each element in the list that follows,...Ch. 15 - Great variation exists in the mechanisms by which...Ch. 15 - Many genes whose expression is turned on by DNA...Ch. 15 - Prob. 29PCh. 15 - The E.coli MalT protein is a positive regulator of...Ch. 15 - Prob. 31PCh. 15 - To find genes that are turned on or off in...Ch. 15 - Prob. 33PCh. 15 - Prob. 34PCh. 15 - Prob. 35PCh. 15 - The researchers who investigated bioluminescence...Ch. 15 - Prob. 37PCh. 15 - Quorum sensing controls the expression of...
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- 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…arrow_forwardThe lac operon consists of three structural genes, lacZ, lacY and lacA that are transcribed as a single polycistronic mRNA. You are given a new strain of Escherichia coli with the following lac operon genotype: p+0°Z•Y*A +// P*O*Z*Y+ A- (i) Explain how the lac I gene affects gene expression. (ii) Explain the function of the lacP in the bacterial operon. (iii) Which part of the lac operon is cis-dominant? Explain.arrow_forwardLet’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation may block the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operon in a way that prevents the repressor protein from binding to the operator. How would you distinguish between these two possibilities?arrow_forward
- The symbols A, B, C, D, E represent all the components of the lac operon, excluding LacA. The symbols are not in the order of the lac operon. Minus and plus signs represent activity of lacZ or LacY in the absence or presence of IPTG. LacI+ or LacI-, and LacO+ or LacOC alleles were used. Which of the symbols represents each of the lac operon components?arrow_forwardLet’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation mayblock the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operator in a way that prevents lac repressor from binding to the operator. How would you distinguish between these two possibilities?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_forward
- 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_forwardYou 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?arrow_forwardStrain ROFL4 has a premature stop mutation in the lacZ gene, resulting in a nonfunctional b-galactosidase. Otherwise all other parts of the operon are functional. 1. Can strain ROFL4 metabolize lactose if it is present? 2. If lactose is absent, will strain ROFL4 transcribe its lac operon? 3. If lactose is present, will strain ROFL4 transcribe its lac operon?arrow_forward
- If glucose levels in the cell are high and lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon?arrow_forward1. a) If glucose is not available and lactose is absent from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon? b)If glucose is not available, but lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon? b)arrow_forwardA researcher was trying to determine whether two molecules (A and B) were corepressors or inducers in their respective operon systems. Data was collected regarding the levels of protein and the amount of gene transcription for the genes in their respectiver operons. The data is shown below. Level of protein Transcription of gene 1 Transcription of gene 2 low Molecule A High low Low high high Molecule B High high high Low low low a) Determine whether molecule A and Molecule B are inducers or corepressors. Justify your answer. b) Identify which system resembles the lac operon system and which resembles the trp operon system.arrow_forward
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