LECTURE 3 (Regulation of gene expression) Flashcards
(41 cards)
What is the main function of regulating gene expression?
Maintaining the functional integrity of the cell
What is cancer?
A disease of the genome at the cellular level that may be manifested by alterations in gene expression
What must happen to DNA to make it accessible to RNA Polymerase?
Eukaryotic DNA packaged in chromatin structures -> gene expression requires chromatin remodelling -> makes desired gene region accessible to RNA Polymerase and other proteins required for gene expression
Wha are the primary regulators of gene expression?
Transcription Factors
What is important about Transcription factors?
- Can affect transcription directly by controlling function of RNA polymerase or indirectly by affecting chromatin structure
- Contain at least 2 recognisable domains
[DNA-BINDING DOMAIN and an ACTIVATION DOMAIN]
What are Transcription Factors?
Proteins that can bind specific DNA sequences and regulate gene expression
What are DNA binding motifs?
DNA binding proteins that make specific contacts to dsDNA molecule without breaking the hydrogen bonds -> Contacts occur between the DNA binding proteins and the edges of the base pairs that are exposed in the grooves of the DNA (especially MAJOR GROOVE)
Describe the Zinc finger motif
- Domain is configured around a ZINC ATOM that links TWO CYSTEINES and TWO HISTIDINES
- Consists of a simple ββα fold
- Side chains of specific amino acids recognise a specific DNA sequence
What is the function of the Activation domain?
- Bind to other transcription factors and co-regulators
- Recruit chromatin-modifying proteins such as HISTONE ACETYLASES or DEACETYLASES
What is a Co-activator?
A type of transcriptional co-regulator that binds to a transcription factor to increase the rate of transcription of a gene or set of genes
Which coactivator is often over expressed in breast cancer?
The steroid receptor coactivator (SCR) NCOA3
What are the two main types of transcription factors?
- General transcription factors
- Sequence-specific transcription factors
What is the function of General transcription factors?
Interact with RNA Polymerase, forming the initiation complex required for the initiation of transcription
Which general transcription factors does RNA Polymerase II need?
TFIIA, B, D, E, F and H
What are sequence-specific transcription factors?
DNA-binding proteins that recognise specific nucleotide sequences and regulate gene expression
Describe the function of Sequence-specific transcription factors
- Can act positively to promote TRANSCRIPTION or negatively to promote GENE SILENCING
- In eukaryotic cells, RNA polymerase cannot recognise promoter sequences themselves -> task of gene-specific factors to create a local environment to attract general factors -> attract polymerase
What are Co-activators/Co-repressors?
Proteins that bind to the sequence-specific transcription factors and modulate their function by repressing or activating gene expression
What are the major characteristics of Cyclic AMP response element binding protein 1 (CREB)?
- General transcription factor
- Expressed in all nucleated cells
- Overexpressed in HEMATOPOIETIC and SOLID TUMOURS compared with control tissues -> identification of CREB associated cancers
What is Activating Protein-1?
A transcription factor important for the processes of growth, differentiation and death playing a role in carcinogenesis
What are the properties of Activating Protein-1?
- Composed of two components and can be produced by dimers of proteins from the Jun and For families
- Activated AP-1 can bind to a specific DNA sequence “5’-TGAG/CTCA-3’” which is located in the promoter and therefore regulates the transcription of downstream target genes
Describe the regulation of gene expression by the oestrogen receptor and by small-molecule modulators of ER function
1) Oestrogen steroid hormone ESTRADIOL binds to the ligand binding domain (LBD) of the ER to induce a CONFORMATIONAL CHANGE -> facilitates co-activator recruitment and activation of gene expression
2) Binding of a selective oestrogen receptor modulator (SERM) to the LBD blocks co-activator recruitment -> blocks gene activation
3) Binding of a selective oestrogen receptor degrader (SERD) promotes PROTEASOME-MEDIATED DEGRADATION of the ER -> blocks gene activation
Describe Chromatin structure
- Human DNA present in nucleus of cells in the form of 46 chromosomes
- Chromatin: a thread of DNA (60%), associated RNA (5%) and protein (35%)
- Simplest organisation = beads on a string array
What are Histones?
A group of basic protein that associate with DNA and help the DNA to condense into chromatin
Describe the structure of histones
Large proportion of +ve charged amino acids (Lysine + Arginine) -> DNA is -ve charged due to phosphate groups on its backbone -> Strong attraction between opposite charges -> High affinity binding between histone and DNA -> Nucleosome
