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Regulation of Transcription
C483 Spring 2013
1. Which of the following is true about transcription regulation?
A) A repressor protein activates transcription of a negatively regulated gene.
B) A positively regulated gene can be transcribed only in the absence of active
repressor.
C) In the absence of an activator, a negatively regulated gene is poorly
transcribed.
D) The initiation of transcription of regulated genes is controlled by regulatory
proteins which bind to specific DNA sequences.
E) All of the above.
2. Protein X is found to bind to a certain gene's promoter only when substance
A is not present. The gene can be transcribed in the presence of both X and A.
It is not transcribed in the presence of X alone. Protein X is a(n) ________.
Substance A is a(n) ________.
A) repressor; inducer
B) repressor; corepressor
C) activator; inducer
D) activator; corepressor
3. An operon is ________.
A) a set of genes whose transcription is controlled by a single promoter
B) the site of repressor binding
C) a protein that activates the transcription of a whole class of genes
D) a multisubunit complex responsible for the splicing of exons
4. Which of these is not part of the lac operon?
A) An enzyme that hydrolyzes b-galactosides
B) Galactoside permease
C) Lac repressor
D) An enzyme that marks unusable galactosides
Regulation
• Housekeeping genes—constitutive
• Regulation of gene expression can occur at
any point of information flow, but occurs most
often at level of transcription
• Positive regulation requires Activator
• Negative regulation controlled by Repressor
• Regulation proteins are often allosteric
– Inducers and corepressors
Lac Operon
• Example of “simple” regulation at the level of
transcription
• Both positive and negative regulation
– DON’T NEED TO KNOW REGULATION DETAILS
• Goal: understand an example of why
regulation is necessary and useful
– First three paragraphs of 21.7
E. Coli and Fuel Sources
• Prefer glucose; can use b-galactosides
(lactose)
• Only synthesize metabolic enzymes for
lactose if lactose is present and glucose low!
• Three necessary proteins
– Transporter
– Cut useful galactosides
– Mark nonuseful galactosides
Operon
• Three genes for three proteins controlled by
single promoter region (operon)
Lac repressor (not
part of operon)
B-galactosidase
(hydrolyse
lactose)
Lactose
permease
Thiogalactoside
transacetylase
Regulation
• Very tight repressor
binding
• Rare spontaneous
release allows for one
transcription by
promoter that is poise
• “escape synthesis”
• Low level of permease
available to allow
lactose to enter cell
O = “operator”
Answers
1.
2.
3.
4.
D
A
A
C