You are studying the ABCD operon from a newly isolated bacterium. Which of the following would result in expression of proteins A, B, and C but not D? C promoter Mutation in D that causes degradation of the mRNA Mutation in A that removes the translational start site All of these options Mutation of sequences in the promoter needed for RNA Polymerase to bind Insertion of a transcriptional termination site in the beginning of the D sequence

You are studying the ABCD operon from a newly isolated bacterium. Which of the following would result in expression of proteins A, B, and C but not D? C promoter Mutation in D that causes degradation of the mRNA Mutation in A that removes the translational start site All of these options Mutation of sequences in the promoter needed for RNA Polymerase to bind Insertion of a transcriptional termination site in the beginning of the D sequence

Biology 2e

2nd Edition

ISBN:9781947172517

Author:Matthew Douglas, Jung Choi, Mary Ann Clark

Publisher:Matthew Douglas, Jung Choi, Mary Ann Clark

Chapter16: Gene Expression

Section: Chapter Questions

Problem 9RQ: The a/a operon is an inducible operon that controls the production of the sugar arabinose. When...

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You are studying an operon containing three genesthat are cotranscribed in the order hupF, hupH, andhupG. Diagram the mRNA for this operon, showingthe location of the 5′ and 3′ ends, all open readingframes, translational start sites, stop codons, transcription termination signals, and any regions thatmight be in the mRNA but do not serve any of thesefunctions.
. In an effort to determine the location of an operator sitefor a negatively regulated gene, you have made a seriesof deletions within the regulatory region. The extent ofeach deletion is shown by the line underneath the sequence, and the resulting expression from the operon(i = inducible; c = constitutive; − = no expression) isalso indicated.... GGAT C T T AGCCGGCTAACATGATAAATATAA......C C T AGAATCGGCCGA TTGTA C T A TTT ATAT T ...1 i2 –3 c4 –5 ca. What can you conclude from these data about thelocation of the operator site?b. Why do you think deletions 2 and 4 show no expression of the gene?
One of the main lessons of this chapter is that severalbacterial genes are often transcribed from a singlepromoter into a large multigene (polycistronic) transcript. The region of DNA containing the set of genesthat are cotranscribed, along with all of the regulatoryelements that control the expression of these genes, iscalled an operon.a. Which of the mechanisms in the following listcould explain differences in the levels of themRNAs for different operons?b. Which of the mechanisms in the following listcould explain differences in the levels of theprotein products of different genes in the sameoperon?i. Different promoters might have different DNAsequences.ii. Different promoters might be recognized bydifferent types of RNA polymerase.iii. The secondary structures of mRNAs might differ so as to influence the rate at which they aredegraded by ribonucleases.PROBLEMSProblems 575a. Why did the mating with a nonlysogenic recipientresult in phage growth and release, but the infectionof a…
The promoter of an operon is the site to which RNApolymerase binds to begin transcription. Certain basechanges in the promoter result in a mutant site towhich RNA polymerase cannot bind. Would you expect mutations in the promoter that prevent binding ofRNA polymerase to act in trans on another copy ofthe operon on a plasmid in the cell, or only in cis onthe copy immediately adjacent to the mutated site?
A mutant strain has a defective lac operator site that results in theconstitutive expression of the lac operon. Outline an experimentyou would carry out to demonstrate that the operator site mustbe physically adjacent to the genes that it influences. Based onyour knowledge of the lac operon, describe the results you wouldexpect.
You have isolated two different mutants (reg1 andreg2) causing constitutive expression of the emu operon (emu1 emu2). One mutant contains a defect in aDNA-binding site, and the other has a loss-of-functiondefect in the gene encoding a protein that binds tothe site.a. Is the DNA-binding protein a positive or negativeregulator of gene expression?b. To determine which mutant has a defect in the siteand 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 Emu1and Emu2 proteins, what results do you predict forthe two strains (i and ii; see descriptions below) ifreg2 encodes the regulatory protein and reg1 is theregulatory site?i. F′ (reg1−reg2+emu1−emu2+)/reg1+reg2+emu1+emu2−ii. F′ (reg1+reg2−emu1−emu2+)/reg1+reg2+emu1+emu2−c. What results do you predict for the two strains(i and ii) if reg1 encodes the regulatory proteinand reg2 is the regulatory site?
Attenuation of the trp operon is regulated by the efficiency of translation of the trp leader (trpL).A scientist mutates the aminoacyl tRNA synthetase responsible for charging tRNATrp, resulting in1/100 the normal amount of charged tRNATrp. How would this mutation impact attenuation ofthe trp operon? Explain why.
Mutations in bacterial promoters may increase or decrease therate of gene transcription. Promoter mutations that increasetranscription are termed up-promoter mutations, and those thatdecrease transcription are termed down-promoter mutations.The sequence of the −10 site of the promoter for the lac operonis TATGTT (see Figure 14.5). Would you expect each of thefollowing mutations to be an up-promoter or down-promotermutation?A. TATGTT to TATATTB. TATGTT to TTTGTTC. TATGTT to TATGAT
Suppose that you have isolated a mutant strain of E. coli inwhich the lac operon is constitutively expressed. To understandthe nature of this defect, you create a merozygote in which themutant strain contains an F′ factor with a normal lac operonand a normal lacI gene. You then compare the mutant strain andthe merozygote with regard to their β-galactosidase activities inthe presence and absence of lactose. You obtain the followingresults:
Lactose permease is encoded by the lacY gene of the lac operon.Suppose a mutation occurred at codon 64 that changed the normalglycine codon into a valine codon. The mutant lactose permease isunable to function. However, a second mutation, which changescodon 50 from an alanine codon to a threonine codon, is able torestore function. Is each of the following terms appropriate or inappropriate to describe this second mutation?A. ReversionB. Intragenic suppressorC. Intergenic suppressorD. Missense mutation
The figure at the beginning of this chapter showsthe binding of both a Lac repressor tetramer and aCRP-cAMP complex to the regulatory region of thelac operon.a. What is the key feature of a regulatory protein suchas the Lac repressor or CRP that allows it to regulate specifically the genes or operons it is supposedto control?b. On the figure, show the positions of the followingcomponents: (i) A Lac repressor monomer; (ii) a Lacrepressor dimer; (iii) all four DNA binding domains ofthe Lac repressor tetramer; (iv) a single helix-turnhelix motif; (v) the o1 part and either the o2 or o3 partsof the lac operator (assume the operon would be transcribed from right to left on the figure); (vi) themultimerization domains of the four Lac repressormonomers; (vii) an inducer-interacting domain; (viii)the CRP-cAMP complex; and (ix) a DNA loop.c. What is the physical basis for the formation of theDNA loop shown in the figure?d. On the figure, show the position of two axes ofsymmetry in the sequence…
a. The original constitutive operator mutations in thelac operon were all base changes in o1. Why doyou think mutations in o2 or o3 were not isolated inthese screens?b. Explain how a mutagen that causes small insertions could produce an ocmutation.c. Would a strain with one of the ocmutations described in part (b) and also a lacIS mutation be ableto make β-galactosidase either in the presence orabsence of inducer? Explain