Regulation Of Transcription Initiation

Question 1

How is the assembly of the transcription complex regulated?

Answer 1

A major part of regulation involved binding of activator and repressor proteins to specific DNA sequences. Many activator proteins also bind to Mediator , which helps RNA polymerase bind to the promoter

Question 2

What do cis-regulatory elements do?

Answer 2

. Increase or decrease basal level of expression. Level of transcription
. Specify responses to particular signals- these cisregulatory elements are called response elements (controls the way gene elements respond to a particular signal. They do not regulate themselves but the gene they are in)

Question 3

Metallothioneins (gene) bind to metal ions. What are it’s two functions?

Answer 3

. Bind toxic metal ions and so protect organisms from their effects
. Store and buffer needed metal ions, such as Zn2+

Question 4

In humans what is transcription induced by?

Answer 4

. Metal ions (e.g. Zn2+)
. Glucocorticoid hormone (associated with stress), turns the gene on, probably because you need the resources. (These act independently of each other)

Question 5

What are the cis-regulatory elements involved in human metallothionein gene transcription and it’s regulation?

Answer 5

. TATA: the TATA box
. E-box, BLE, TRE, GC: increase general level of expression of the gene/ the overall level of transcription
. Response elements-control response to particular signals:
- MRE: response to metals. Presence of several elements gives greater response than one
- GRE: response to glucocorticoid hormone

Question 6

Each cis-regulatory element binds to specific transcription factors (activator proteins. Which one binds to which one?

Answer 6

. AP2 (activator protein 2) binds to BLE
. AP1 binds to TRE
. SP1 binds to GC box
. USF binds to E-box
. MTF1 binds to MRE when activates by binding Zn2+ (Zn2+ ion binds to an activator protein, causing it to bind to the MRE)
. Glucocorticoid receptor binds to GRE when activated by binding glucocorticoid hormone

Question 7

See page 43 for a good summary

Answer 7

…

Question 8

Define a core promoter

Answer 8

Where RNA polymerase binds. Different core promoters contain different combinations of defined ‘elements ‘

Question 9

Define a proximal promoter

Answer 9

Region near core promoter containing cis-regulatory elements

Question 10

Define enhancers

Answer 10

Cis-regulatory elements far from the core promoter

Question 11

What system are hormones produced in an animal?

Answer 11

The endocrine system

Question 12

Some hormones enter the cell and exert their effects directly: small molecule with fairly hydrophobic structures that can easily cross cell membranes. These include:

Answer 12

. Adrenal steroids (produced by adrenal gland), such as glucocorticoids (e.g. cortisol)
. Steroid sex hormones- androgens oestrogens

Question 13

The principal glucocorticoid hormone is cortisol. What is it’s purpose?

Answer 13

. Cortisol is released during starvation or intense exercise
. It binds to glucocorticoid receptor (GR)
. Major physiological effects:
- increases blood sugar
- also has anti-inflammatory and immunosuppressive action (due to inhibition of transcription)

Question 14

Give examples what some of the naturally-occurring mutations in the glucocorticoid receptor are associated with

Answer 14

. Raised body mass index (affects metabolic rate)

. Beneficial body composition in young adults and greater muscle strength in young men

Question 15

The response cortisol has on a cell depends on cell type. How does it affect liver cells?

Answer 15

In liver cells cortisol increases glucose production via gluconogenesis from amino acids and other small molecules.

Question 16

See bottom of page 45

Answer 16

…

Question 17

Receptors for steroid hormones, thyroid hormones, and retinoic acid constitutive ‘superfamily’ of ligand-responsive transcription factors. All have similar structures and all:

Answer 17

. Bind to DNA
. Interact with the transcription complex to regulate transcription
. Are made up of domains (regions of the protein) with distinct functions 1

Question 18

Describe the mechanism of transcription activation by glucocorticoids

Answer 18

1. In absence of hormone, a protein called hsp90 keeps the glucocorticoid receptor in the Custodio. Hsp90 is a chaperone protein: general role of chaperones is to prevent inappropriate interactions. Prevents transcription when not needed)
2. Glucocorticoid hormone enters cell by diffusion
3. Hormone binds to glucocorticoid receptor in the custodial. Binding of hormone causes hsp90 to dissociate
4. Glucocorticoid receptor contains a nuclear localisation signal, which is masked by hsp90. When hsp90 dissociates from the glucocorticoid receptor, moves into the nucleus
5. Receptor binds to glucocorticoid response element (GRE) in genes such as those for tyrosine aminotransferase and PEP carboxykinase and activates transcription

Question 19

Bottom of page 46 and top and middle bit about response elements of page 47. Summary on page 48

Answer 19

…

Question 20

What are steroid hormone receptors?

Answer 20

Zinc finger proteins- loops of amino acids stabilised by Zn2+ ions

Question 21

What are the functions of zinc fingers?

Answer 21

1. Binding to DNA. Amino acids in the recognition helix interact with bases in DNA
2. Dimer formation

Question 22

What does the glucocorticoid receptor probably do?

Answer 22

. Promotes chromatin remodelling, including repositioning of nucleosomes to allow other transcription factors to bind
. Binds to mediator, helping RNA polymerase bind to the promoter

Question 23

What does AP1 do?

Answer 23

Increases general chromatin accessibility and helps glucocorticoid receptor to bind to the GRE. A dominant negative mutant can’t bind to DNA and so doesn’t increase chromatin accessibility

Question 24

Not all cells respond to a hormone, what is one explanation for this?

Answer 24

Liver cells don’t respond to progesterone because they don’t contain progesterone receptor so, can’t respond