16. Regulation of Expression

Eukaryotic Transcriptional Control

Which of these statements about enhancers is correct?
a. They contain a unique base sequence called a TATA box.
b. They are located only in 5′ untranslated regions.
c. They are located only in introns.
d. They are found both upstream and downstream from the transcription start site and are functional in any orientation.

Gene Regulation in Eukaryotes Part 2

 No. Mitochondria are not involved in the expression of most genes. 

 No. DNA polymerase is involved in DNA replication, not gene expression. 

 No. This is unlikely because the same set of histones is bound to all genes. 

Think about molecules that enter the cell and become part of the transcription factor complex.

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of causing cancer and birth defects in animals and humans. It apparently acts by entering cells and binding to specific proteins, which then enter the nucleus and alter the pattern of gene expression. Therefore, dioxin acts by mimicking the action of __________.

Regulatory segments of DNA that function to increase transcription levels in eukaryotes are called:

Introduction to Transcription Factors

 stimulating a receptor on the surface of muscle cells, thus activating a signal-transduction pathway that promotes muscle development 

 No. MyoD is a transcription factor that binds to enhancers directly in the DNA. 

 increasing the translation of muscle-related genes 

 No. Genes are transcribed, not translated. 

 stimulating the production of muscle-specific splicing variants of certain mRNAs 

 No. MyoD acts as a transcription factor to stimulate the transcription of genes. It does not act at the RNA level. 

 enhancing apoptosis of non-muscle cells 

 No. There is no evidence that MyoD stimulates apoptosis in non-muscle cells. 

 turning on the expression of multiple muscle-related genes 

The myoD gene is referred to as a master regulatory gene.

MyoD promotes muscle cell development by __________.

Enhancers are transcription factors; proximal control elements are DNA sequences.

Enhancers increase transcription of specific genes; proximal control elements inhibit transcription of specific genes.

Enhancers are located thousands of nucleotides away from the promoter; proximal control elements are close to the promoter.

Enhancers are DNA sequences; proximal control elements are transcription factors.

Which of the following statements correctly describes the primary difference between enhancers and proximal control elements?

 the binding of general transcription factors to the TATA box within the promoter of a gene 

 No. This alone typically leads to low rates of gene transcription. 

 the coordinated control of genes within operons 

 No. Operons are not found in eukaryotes. 

 specific binding of activator molecules to enhancers 

 No. This can contribute to higher rates of gene transcription, but there is a better answer. 

 protein-protein interactions that are promoted by the activation domains of activator proteins 

 The third and fourth listed responses are correct. 

How do protein-protein interactions promote the integration of proximal and distal control elements for a gene?

A high rate of gene transcription in eukaryotic cells is usually dependent on __________.

Compare and contrast the items in each pair: (a) enhancers and the E. coli CAP binding site

 No. This statement is true, but there is a better response. 

 may be located upstream or downstream from the genes they regulate 

 may be located thousands of base pairs away from the promoter 

 All of the listed responses are correct. 

Enhancers are distal control elements.

Enhancers __________.

General Transcription Factors

Eukaryotic gene expression regulation: concept of chromatin

 No. Histones are a type of protein that is bound to the DNA, forming nucleosomes. 

 No. Eukaryotic activators do not usually bind directly to promoter DNA. 

 No. Silencing is the process of inhibiting transcription, not stimulating it. 

What are some of the regulatory sequences found in the eukaryotic genome?

In a eukaryote, transcription factors called activators may stimulate gene expression by binding to DNA sites called __________.

Gene Regulation in Eukaryotes Part 1

The Hawaiian bobtail squid (Euprymna scolopes) is able to glow from luminescent Vibrio fischeri bacteria held in its light organs. As it swims at night near the ocean surface, it adjusts the amount of light visible to predators below to match the light from the stars and moon. Predators have difficulty seeing the illuminated squid against the night sky. The bacteria glow in response to a molecule that regulates expression of genes involved in light-producing chemical reactions. The regulator controls production of the genes’ mRNA. Therefore, the light-producing genes are under
a. transcriptional control.
b. translational control.
c. post-translational control.
d. negative control.

The functioning of enhancers is an example of
a. a eukaryotic equivalent of prokaryotic promoter functioning.
b. transcriptional control of gene expression.
c. the stimulation of translation by initiation factors.
d. post-translational control that activates certain proteins.

Specific Transcription Factors

Compare and contrast the items in each pair: (c) general transcription factors and sigma.

In eukaryotes, what allows only certain genes to be expressed in different types of cells?

The transcription initiation complex is composed of RNA polymerase, general and specific transcription factors.

General transcription factors help initiate transcription of all eukaryotic genes.

Specific transcription factors do not bind the promoter of a gene, but to control elements associated with the gene.

The transcription initiation complex associates with the TATA box of the promoter to begin transcription.

Which of the following statements about transcription factors is incorrect:

The light-producing genes of V. fischeri are organized in an operon that is under positive control by an activator protein called LuxR. Would you expect the genes of this operon to be transcribed when LuxR is bound or not bound to a DNA regulatory sequence? Explain.

Compare and contrast the items in each pair: (b) promoter-proximal elements and the operator of the lac operon

Eukaryotes use multiple transcription factors to help initiate transcription.

Most eukaryotes have regulatory sites that are close to their promoters.

Most prokaryotes transcribe multiple genes under the regulation of a single operon.

Prokaryotic transcription factors usually interact directly with RNA polymerase while eukaryotic transcription factors do not.

Which of the following is NOT true regarding the differences of transcription in eukaryotes and prokaryotes?

Gene Regulation in Eukaryotes

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