CSB349H1 Lecture Notes - Lecture 5: Transferase, Transcription Factor Ii H, Radioactive Tracer
14 May 2018
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Lecture 5(b): Transcription III
Mediator Complex:
• Consists of 25-30 separate subunit proteins
• Mediator complex is not required for initiating transcription in vitro
o However does play a role for allowing full transcription
(efficiency and processivity)
§ Allows us to obtain robust gene expression
ð Mediator complex is recruited by transcription factors to the
proximal promotor
o Mediator containing sequence specific TFs will allow it
to interact with the general transcription factors found
in TSS
Mediator Function:
• Mediates information between the activators (bound to
enhancers & promotors) and initiation complex
o Serves as a bridge between activator and initiation complex
ð Mediator function as the recruitment step:
o Stabilizing activator-dependent re-initiation intermediates allowing for multiple
rounds of transcription from an initial PIC
• Some transcription actors are capable of interacting with the RANPII without the mediator
o However, some TFs can only function through the communication with the mediator
to allow for complete transcription
§ If the mediator is absent => transcription is drastically reduced
• If core promotor is mutated (deleted) the RNAPII will no longer be recruited; no transcription
o Mediator will still go to those genes; due to the sequence-specific TF
Initiation of Transcription:
1. Phosphorylation of CTD – RNAPII
o CTD is composed of tandem repeats of a conserved heptad amino acid sequence
(YSPTSPS) => 52 times in vertebrates |26 times in yeast
o TFIIH has a Cdk7-cyclinH (kinase) functions to phosphorylate serine 5 on CTD
§ Phosphorylation leads to the recruitment of capping factors and allows
transcription of ~50bp of RNA
2. Methylation of H3K4
o Set1 complex functions to methylate lysine 4 on histone 3
§ Essential for initiating transcription
• Other histone modifications are also associated with initiation
ð Regions where transcription takes place we observe H3K4 methylation; via ChIP
Document Summary
Lecture 5(b): transcription iii: consists of 25-30 separate subunit proteins, mediator complex is not required for initiating transcription in vitro, however does play a role for allowing full transcription (efficiency and processivity) Allows us to obtain robust gene expression. Mediator complex is recruited by transcription factors to the proximal promotor: mediator containing sequence specific tfs will allow it to interact with the general transcription factors found in tss. Mediator function: mediates information between the activators (bound to enhancers & promotors) and initiation complex, serves as a bridge between activator and initiation complex. If the mediator is absent => transcription is drastically reduced. If core promotor is mutated (deleted) the rnapii will no longer be recruited; no transcription: mediator will still go to those genes; due to the sequence-specific tf. Phosphorylation leads to the recruitment of capping factors and allows transcription of ~50bp of rna: methylation of h3k4, set1 complex functions to methylate lysine 4 on histone 3.
