11.3 - The activity of positive regulatory transcription factors: repressors Flashcards
What are ways that repressors can control transcription?
- sequester activator in the cytoplasm - repressor binds to domain that allows protein to transport through nuclear membrane
- repressor binds to
an activator that is already bound to an enhancer and masks its activation domain - can be masked and held in cytoplasm until needed
- can compete with activator for an enhancer
Are the DNA-binding domain and activation domains dependent of e/o?
- No, the activation domain interacts with the basal apparatus irrespective of DNA location
- As long as DNA is present, the activation domain can be brough to the basal apparatus
What is the two-hybrid assay?
- Works by testing the ability of two proteins to interact where one has a DNA-binding domain and the other has a transcription-activation
domain.
What is the result of this test?
- If the tested proteins can interact, then the hybrid proteins will interact
How does activation occur in this test?
- Protein w/ DNA-binding domains binds to reporter gene but does not activate gene
- Activation occurs only if second hybrid binds to first hybrid to bring activation domain to promoter
How do activators interact w/ basal apparatus?
- Through the use of DNA-binding domain which searches for an activation domain that it covalently attaches to and is close to the basal apparatus
- Activators should have a DNA-binding and a activation domain
What role does the activation domain play?
- contacts w/ transcriptional factors that promote basal apparatus assembly
What happens when an activator does not have an activation domain?
- A coactivator is then needed to bind the activator to the basal apparatus
What are some basal factors that activators contact with?
- TF D, TF B, or TF A
- TF D is the most common ana it may contact on of several TAFs (TAFs provide connection between activators and basal apparatus)
What is another component that may be required for activators to stimulate transcription?
- RNA polymerase may be associated with various
alternative sets of transcription factors in the form of a holoenzyme complex - Mediator complexes associate with RNA polymerase and replace activators/co-activators
and basal factor
What are the types of DNA-binding domains?
- Zinc finger
- Steroid receptor
- Helix-turn-helix
- Homeodomain
- Helix-loop-helix
- Leucine zipper
- bZIP (“basic zipper”)
What is the zinc finger?
DNA-binding motif that typifies transcription factors
- made up of Cys and His residues
What is the steroid receptor?
- transcription factors that are activated by binding of a steroid ligand
What is the helix-turn-helix?
- the motif that describes an arrangement of two α-helices that form a site that binds to DNA, one fitting into the major groove (C-terminal) of DNA and the other in the minor groove (N-terminal)
What is the homeodomain?
- DNA-binding motif that typifies a class of transcription factors
- can be activators or repressors
What is the helix-loop-helix?
- hydrophobic residues on one side and charged residues on the other side
- motif enables proteins to dimerize, either homodimers or
heterodimers, and a basic region near this motif contacts DNA - Not all of the HLH proteins contain a DNA-binding domain, but rather rely on their partner for sequence specificity.
What is the leucine zipper?
- A dimerization motif that is
found in a class of transcription factor
What is the bZIP (basic zipper)?
- a bZIP protein has a basic
DNA-binding region adjacent to a leucine zipper dimerization motif
What is chromatin remodeling?
- Inducing charges in chromatin structure
- the energy-dependent displacement or reorganization of nucleosomes that occurs
in conjunction with activation of genes for transcription
What type of energy is used in chromatin remodeling?
- energy provided by ATP hydrolysis
How are remodeling complexes categorized and how does it take form? (COME BACK)
- grouped into ATPase catalytic subunit
- Remodeling complexes can alter, slide, or displace nucleosomes
- displacing histones
