For some time it was not clear whether lac repressor inhibits lac operon transcription by inhibiting the binding of RNA polymerase to its pro- moter or by allowing transcription initiation but blocking elongation past the site of bound repressor. How might you distinguish between these possibilities?

For some time it was not clear whether lac repressor inhibits lac operon transcription by inhibiting the binding of RNA polymerase to its pro- moter or by allowing transcription initiation but blocking elongation past the site of bound repressor. How might you distinguish between these possibilities?

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter10: From Proteins To Phenotypes

Section: Chapter Questions

Problem 21QP: Transcriptional regulators are proteins that bind to promoters (the 5-flanking regions of genes) to...

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For some time, it was not clear whether lac repressor inhibits lac operon transcription by inhibiting the binding of RNA polymerase to its promoter or by allowing transcription initiation but blocking elongation past the site of bound repressor. How might you distinguish between these possibilities?
Mechanisms that inhibit TE activity include theproduction of transposition repressors throughalternative splicing and the action of _________ thatblock TE transcription.
Many transcriptional activators are proteins with a DNA-binding domain (DBD) and an activation domain (AD). Explain how each domain contributes to transcriptional initiation. Would you expect repressors to also have each of these domains?
How does the binding of the trp corepressor and the lac inducer to their respective repressor proteins alter repressor function and transcription in each case? What if there was a mutation in the operator region of the lac operon and the active repressor could not bind there? How would this affect the cell’s production of β–galactosidase? In general, Histone acetylation makes DNA ___________________, while DNA methylation makes DNA ________________.
Some compounds called antiinducers bind to repressors such as the lac repressor and inhibit the action of inducers; that is, transcription is repressed and higher concentrations of inducer are required to induce transcription. Propose a mechanism of action for anti-inducers.
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 a new mutation lacIes, ('es' stands for ‘extra-strength’) has been discovered in the lac operon that allows the lac-repressor to bind even to the lacOc operator. Other properties of lacIes repressor remain normal (that is the same as of lacI+). Given this genotype Is P+ Oc Z+ Y- / Ies P+ O+ Z+ Y+ , under which conditions will the gene lacZ be transcribed to produce β-galactosidase and the gene lacY transcribed to produce permease? A) With lactose, β-galactosidase and permease are produced, without lactose they are not produced B) With lactose, β-galactosidase is produced, without lactose it is not; permease is never produced C) β-galactosidase is always produced and permease is never produced D) With lactose, β-galactosidase and permease are produced, without lactose they are also produced E) β-galactosidase is always produced and permease is produced only in the presence of lactose
. An interesting mutation in lacI results in repressorswith 110-fold increased binding to both operator andnonoperator DNA. These repressors display a “reverse”induction curve, allowing β-galactosidase synthesis inthe absence of an inducer (IPTG) but partly repressingβ-galactosidase expression in the presence of IPTG. Howcan you explain this? (Note that, when IPTG binds a repressor, it does not completely destroy operator affinity,but rather it reduces affinity 110-fold. Additionally, ascells divide and new operators are generated by thesynthesis of daughter strands, the repressor must findthe new operators by searching along the DNA, rapidlybinding to nonoperator sequences and dissociating fromthem.)
Compare and contrast the transcriptional regulation of GAL genes in yeast with that of the lac genes in bacteria.
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?
Describe the binding of RNA polymerase, repressors, andactivators to the lac operon when both lactose and glucose are scarce. What is the effect of these scarcities ontranscription of the lac operon?
Explain how the data shown indicate that two operator sites are necessary for repression of the lac operon. What would the results have been if all three operator sites were required for the binding of lac repressor?