GENE REGULATION IN EUKARYOTES

Mediator

-is a protein complex -another way regulatory transcription factors can control RNA Pol II -mediator mediates the interaction between RNA pol II and regulatory transcription factors -controls ability of RNA POL II to progress to the elongation stage of transcription (via phosporylation of the carboxyl terminal domain) -this facilitates switch from initiation to elongation stage ACTIVATOR- binds to distant enhancer activator and mediator are brought together by formation of a loop within the intervening DNA REPRESSOR- repressor proteins prevent mediator from allowing RNA POL II from proceeding to elongation phase of transcription

3rd way regulatory transcription factors influence transcription is by recruiting proteins to the promoter region

-this affects nucleosome positions and compositions -certain transcriptional activators recruit proteins to the promoter region that alter chromatin structure

What is the effect of binding regulatory transcription factors to regulatory elements?

Affects the transcription of an associated gene -may enhance or inhibit rate of transcription -activator- enhancer -repressor- silencers

Combinatorial control

Eukaryotic genes are regulated by many factors

Do regulatory transcription factors bind directly to RNA pol

No, they exert their effects by binding to regulatory elements to influence their function

Transcription factors

Proteins that influence the ability of RNA POL to transcribe a given gene -regulate binding of transcriptional complex to core promoter -control the switch from the initiation to the elongation stage of transcription 2 main types: 1. General transcription factors -required for binding RNA Pol to core promoter and its progression to the elongation stage 2. Regulatory transcription factors -regulates the rate of transcription of nearby genes -influence ability of RNA Pol to begin transcription of a particular gene -recognize cis regulatory elements located near core promoter (cis regulatory elements are response elements, control elements, regulatory elements) -binding regulatory transcription factors to regulatory elements will affect the transcription of the associated gene

Regulatory transcription factors may exert their effects through TFIID and Mediator

These mechanisms explain how regulatory transcription factors bind to a regulatory element to affect transcription -net affect of a regulatory transcription factor is to influence the ability of RNA Pol II to transcribe a given gene

What is the net affect of a regulatory transcription factor?

To influence the ability of RNA Pol II to transcribe a given gene

TFIID

is a general transcription factor that binds to the TATA box -is needed to recruit RNA Pol II to the core promoter Activators- proteins expected to enhance the ability of TFIID to initiate transcription - proteins can help TFIID bind to TATA box -Proteins can enhance the function of TFIID to allow it to facilitate its ability to recruit RNA Pol II -Can bind with a COACTIVATOR (used to increase rate of transcription but doesn't directly bind to DNA itself) -Coactivator contains TRANSACTIVATION domain (this promotes activation of RNA pol by acting with general transcription factors) Repressors- inhibit function of TFIID -proteins prevent binding of TFIID to TATA box -Proteins inhibit the ability of TFIID to recruit RNA POL II to TATA BOX at the core promoter