lecture 4 - gene regulation Flashcards
Describe the control of gene transcription
Not all genes are active or transcribed in any
particular cell.
• Differential gene expression to a large extent
determines the proteins that are made in a cell and
therefore determines the type of cell.
When and where a gene is transcribed is regulated by
the interaction of regulatory regions of DNA (cisregulatory elements) with trans-acting factors.
What are cis-regulatory elements?
Specific sequences of DNA involved in regulating
transcription, includes the promoter, enhancers and
silencers.
What are trans-acting factors?
Trans-acting factors associate with cis-regulatory
elements and regulate gene transcription.
What are transcription factor proteins?
trans-regulators that bind directly to DNA or associate with complexes of proteins bound to DNA
What is the role of the promoter region?
Transcription of a protein coding gene requires the
binding of RNA polymerase II to the promoter of the
gene.
• RNA polymerase initiates transcription in a complex of
proteins known as general transcription factors.
• Not all general transcription factors bind directly to
DNA
What are general transcription factors?
General transcription factors act in a large complex of proteins known as the Transcription Initiation Complex
• General transcription factors are required for the transcription of all protein coding genes transcribed by RNA polymerase II
• RNA polymerase II is unable to initiate transcription on its own
• Assembly of the Transcription Initiation Complex takes place at the TATA box in the promoter region.
• There are many different general transcription factors with various functions
i) Recognition of the TATA box sequence in the promoter
ii) Recruitment of RNA pol II to the initiation complex
iii) Unwind DNA helix
What are Enhancers and Silencers: Specific transcription
factors?
The activity of the transcription initiation complex at the
promoter is influenced by specific transcription factor proteins bound to cis-regulatory regions of a gene outside the promoter
• Cis-regulatory sequences bound by activator proteins are known as enhancers and promote transcription
• Cis-regulatory sequences bound by repressor proteins are known as silencers and inhibit transcription
• Enhancers and silencers can be several thousand base pairs from the promoter
What are DNA binding transcription factors?
DNA binding transcription factor proteins recognise
and bind to specific sequences of DNA in cisregulatory
elements.
• Transcription factor binding sites are typically 6-12
bases
• 5% to 10% of genes in genome code for proteins
involved in transcriptional regulation.
• There are many families of transcription factors with
different DNA binding specificities.
Describe the integration of regulatory information
Multiple transcription factors bound to the cisregulatory
regions will influence the expression of a
gene.
• Transcription factors bound to enhancers cause DNA
to loop.
• Where and when a gene is transcribed depends on
the integration of regulatory information at the level of
the transcription complex.
Describe differential gene expression
The combination of cis-regulatory elements present in
each gene is different
• Genes are regulated by different sets of transcription
factors bound at their cis-regulatory elements
• The combination of specific transcription factors present in a given cell determines which genes will be expressed in that cell.
What are gene regulatory hierarchies?
Transcription factor will regulate the expression of multiple downstream targets, including other transcription factors
•Transcription factors regulate cascades of gene transcription
What is the organiser graft experiment?
Experiments carried out on early frog embryos demonstrated that cell signalling plays a critical role during development.
Hans Spemann received a Nobel prize for his work in this area.
Transplantation of the frog dorsal blastopore lip results in the formation of a twinned embryo.
Donor embryo injected with non-diffusible cell marker.
Labelled donor dorsal blastopore lip transplanted into unlabelled host
Most of tissue in the secondary axis is host derived.
Graft produces signals that recruit/organize the host tissue to form secondary axis
