MBMB 451A Section One - Fall 2006

---

---

Transcription - Part B 

	Commitment factors figure 21.11 (Genes VIII) 

III.  General transcription factors

	A.  TFIID = TBP +TAFs
		1.  TBP binds the minor groove of the TATA box and kinks DNA figures 21.12 & 21.13  (Genes VIII)
		2.  TAFs interact with the Inr region 
		3.  makes contact with TFIIB and TFIIA
		4.  have 9-12 different TAF proteins bound to TBP
		5.  only TBP is required for basal transcription figure 21.14  (Genes VIII)

	B.  TFIIA
		1.  helps stabilize TBP-DNA interactions
		2.  required for activation and to counteract repression
		3.  not essential in a highly purified system

	C.  TFIIB figure 21.15
		1.  is a single polypeptide
		2.  involved in start site selection
		3.  homologous to a subunit of TFIIIB
		4.  interacts directly with TBP
	
	D.  TFIIF	
		1.  originally identified as a RNAP II associated protein (RAP)
		2.  has sigma like activity
			enhances RNAP II binding to promoter DNA
			and reduces its nonspecific binding to DNA	
		3.  also important for promoter clearance

	E.  TFIIE
		1.  heterodimer (34 & 56 kD)
		2.  can be shown to bind RNAPII directly
		3.  required for recruitment of TFIIH

	F. TFIIH figure 21.19 
		1.  has both 3'-5' and 5'-3 helicase activity which requires ATP hydrolysis
		2.  the 3'-5' helicase activity is essential for promoter opening
			a. there is an ATP requirement for promoter opening
			b. can circumvent by using supercoiled DNA or premelted DNA
				eliminates the need for TFIIH
		3.  the Cdk7 subunit is a CTD kinase and is regulated by another subunit of IIH called cyclin H
			a.  this complex is referred to as CAK (CTD kinase activating kinase)
			b.  can be dissociated from the core TFIIH complex
			c.  is not required for formation of the first phosphodiester bond formation
		4.  TFIIH is also involved in nucleotide excision repair of DNA
			a.  actively transcribed DNA is more readily repaired
			b.  interaction with TFIIE modulates the ATPase, helicase, and kinase activity of TFIIH

	G.  RNA polymerase II holoenzyme 
		1.  core RNAP II
		2.  general transcription factors- usually missing TFIID
		3.  SRB-mediator complex

---

 

Nucleic Acids  |  Methods-Nucleic Acids: Part A and Part B  and Molecular Cloning |  DNA Supercoiling  |  Nucleosome  | Transcription: Part A  |  Higher Ordered Structure  |  Chromatin Transcription  |  Regulation of Transcription  |  Course Material

Webmaster | MBMB Department | Home

Last updated on September 5, 2006.