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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Chapter 16, Problem 6P
The promoter of an operon is the site to which RNA polymerase binds to begin transcription. Certain base changes in the promoter result in a mutant site to which RNA polymerase cannot bind. Would you expect mutations in the promoter that prevent binding of RNA polymerase to act in trans on another copy of the operon on a plasmid in the cell, or only in cis on the copy immediately adjacent to the mutated site?
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The promoter of an operon is the site to which RNA polymerase binds to begin transcription. Certain base changes in the promoter result in a mutant site that RNA polymerase can’t bind. Would you expect mutations in the promoter that prevents binding of RNA to act in trans on another copy of the operon on a plasmid or only in cis on the copy immediately adjacent to the mutated site?
The 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+
A haploid E. coli cell has the genotype I ¯ P+ O+ Z+ Y ¯ where the I ¯ indicates that the repressor protein cannot bind to the operator due to a mutation. Which of the following statements about cells with this lac operon genotype are correct?
I ¯ P+ O+ Z+ Y ¯
Select all that apply.
β-galactosidase will be transcribed constitutively.
The cells are able to import lactose across the cell membrane.
The cells are lac+ and are able to grow on a medium with lactose but no glucose.
RNA polymerase can bind to the promoter.
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_forwardA mutant strain of E. coli has a premature stop mutation in the lacZgene, resulting in a non-functional b-galactosidase. Otherwise, all other parts of the operon are functional. Which component of an F' plasmid will restore normal regulation and function of the lac operon in the resulting partial diploid?arrow_forwardIn the presence of tryptophan and the promoter sequence was mutated such that the RNA polymerase can no longer bind, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the absence of tryptophan and the trpR repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the presence of tryptophan and the trpR repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be constantly expressed"]arrow_forward
- Which of the following statements about the trp operon is false? If a mutation in region 2 prevents the formation of the 2 + 3 loop in the 5’UTR transcription levels will increase. The trp operon is an example of negative repressible operon. Formation of the anti-terminator in the 5’UTR of the trp operon occurs when trp levels are low. In the presence of high trp-tRNA, the genes of the trp operon are not expressed. The role of trp is to bind to the repressor protein and activate it.arrow_forwardBacterial DNA containing an operon encoding three enzymes is introduced into chromosomal DNA in yeast (a eukaryote) in such a way that it is properly flanked by a promoter and a transcriptional terminator. The bacterial DNA is transcribed and the RNA correctly processed, but only the protein nearest the promoter is produced. Can you suggest why?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_forward
- Trp operon of E. coli is an inducible sytem since it turns on in the presence of tryptophan. In most bacteria, protein synthesis is initiated with a modified methionine residue (N-formylmethionine), whereas unmodified methionines initiate protein synthesis in eukaryotes. Both DNA replication and transcription follow a 5’ to 3’ direction of polarity. Write T if the statement is true and write F if the statement is falsearrow_forwardHow will transcription of the E. coli trp (tryptophan) operon be affected by the following manipulations of the leader region of the trp mRNA?(a) Increasing the distance (number of bases) between the leader peptide gene and region 2(b) Increasing the distance between region 2 and region 3(c) Removing region 4(d) Changing several nucleotides in region 3 so that in can base pair with region 4 but not with region 2arrow_forwardWhat would happen if the operator sequence of the lac operon contained a mutation that prevented the repressor protein from binding the operator? (Explain what would happen both in the presence and absence of lactose)arrow_forward
- A researcher engineers a lac operon on a plasmid but inactivates all parts of the lac operator (lacO) and the lac promoter, replacing them with the binding site for the LexA repressor (which acts in SOS response) and a promoter regulated by LexA. The plasmid is introduced into E. coli cells that have a lac operon with an inactive lacZ gene. Under what conditions will these cells produce beta-galactosidase?arrow_forwardIn E. coli, when glucose is present, galactose is used to make a component of the bacterial cell wall. When glucose is absent, galactose is MOSTLY used to make energy, but a little is used to make the cell wall. The enzymes for the conversion of galactose into a cell wall component are transcribed as an operon. The operon is transcribed at a high level when glucose is present and at a low level when glucose is absent. You isolate mutants that do not respond appropriately to the presence or absence of glucose, as summarized below. Galactose incorporation into cell wall strain + Glucose Glucose Wild type High High High Low Mutant 1 High High Mutant 2 Mutant 3 Low Low Mutant 4 None None Mutant 5 High None Mutant 6 None None Which of the above mutants could have a mutation in the repressor for the above operon Mutant 6 Mutant 5 Mutant 1 Mutant 3arrow_forwardIn E. coli, when glucose is present, galactose is used to make a component of the bacterial cell wall. When glucose is absent, galactose is MOSTLY used to make energy, but a little is used to make the cell wall. The enzymes for the conversion of galactose into a cell wall component are transcribed as an operon. The operon is transcribed at a high level when glucose is present and at a low level when glucose is absent. You isolate mutants that do not respond appropriately to the presence or absence of glucose, as summarized below. Galactose incorporation into cell wall strain + Glucose - Glucose Wild type High High High Low Mutant 1 High High Mutant 2 Mutant 3 Low Low Mutant 4 None None Mutant 5 High None Mutant 6 None None Which of the above mutants could have a mutation in the promoter for the operon with enzymes for galactose incorporation into cell wall? Mutant 3 Mutant 2 Mutant 5 Mutant 1arrow_forward
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