15. Gene Expression

During transcription of DNA to RNA:

What happens during the initiation step of DNA transcription?

Which of the following properties is NOT shared by RNA polymerase and DNA polymerase?

During which stage of transcription do the following processes take place? 

1. RNA polymerase binds to the promoter. 

2. The RNA transcript is released. 

3. The RNA transcript extended.

Which of the following is the correct transcript of mRNA for the following DNA template?  

DNA Template: 3'-ATGAAGCCGAGTCAT-5'.

In eukaryotic cells, transcription cannot begin until

a. The two DNA strands have completely separated and exposed the promoter.

b. Several transcription factors have bound to the promoter.

c. The 5′ caps are removed from the mRNA.

d. The DNA introns are removed from the template.

The RNA polymerase enzyme binds to ________, initiating transcription.

a. Amino acids

b. tRNA

c. The promoter sequence

d. The ribosome

In a particular bacterial species, temperature-sensitive conditional mutations cause expression of a wild-type phenotype at one growth temperature and a mutant phenotype at another—typically higher—temperature. Imagine that when a bacterial cell carrying such a mutation is shifted from low to high growth temperatures, RNA polymerases in the process of elongation complete transcription normally, but no new transcripts can be started. The mutation in this strain most likely affects:

a. The terminator sequence

b. The start codon

c. Sigma

d. One of the polypeptides of the core RNA polymerase

The nucleotide shown here is called cordycepin triphosphate. It is a natural product of a fungus that is used in traditional medicines.

If cordycepin triphosphate is added to a cell-free transcription reaction, the nucleotide is added onto the growing RNA chain but then no more nucleotides can be added. Examine the structure of cordycepin and explain why it ends transcription.

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Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called α-amanitin, a toxin that inhibits transcription.

What would you predict to be the immediate outcome of adding α-amanitin to a cell?

a. Reduced DNA synthesis

b. Reduced production of one or more types of RNA

c. Reduced binding of tRNAs to anticodons

d. Reduced rate of translocation of ribosomes translating mRNA

<Image>

Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called α-amanitin, a toxin that inhibits transcription.

α-Amanitin inhibits transcription by binding inside an RNA polymerase to a region other than the active site that catalyzes addition of a nucleotide to the RNA chain. Based on the model of RNA polymerase shown in Figure 17.3, predict how the toxin might function to inhibit transcription.

<Image>

Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called α-amanitin, a toxin that inhibits transcription.

Toxins like α-amanitin are used for research in much the same way as null mutants (Chapter 16)—to disrupt a process and see what happens when it no longer works. Researchers examined the ability of α-amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of α-amanitin, and then tested their activity. The results of this experiment are shown here. These findings suggest that cells treated with α-amanitin will have a reduced level of:

a. tRNAs

b. rRNAs

c. snRNAs

d. mRNAs