Table 1.

Summary of the general transcription factors and RNA polymerase II.

Protein	Subunits	Size (kDa)	Main Binding Partners	Function
TFIID	TBP, 13 TAFs	~1300	promoter, Pol II	Nucleates PIC assembly by binding multiple core promoter elements
TFIIA	TFIIAα, TFIIAβ, TFIIAɣ	35, 19, and 12	TBP, TFIID	Stabilizes the TFIID-DNA interaction; enhances the effects of transcriptional co-activators
TFIIB	TFIIB	33	promoter, TBP, Pol II	Helps to define the start site of transcription and orient Pol II in the proper direction
TFIIF	RAP30, RAP74	30 and 74	promoter, Pol II, GTFs	Guides Pol II to the PIC and facilitates elongation
Pol II	Rpb1–Rpb12	~514	promoter, all GTFs	Catalyzes RNA synthesis; phosphorylation of the CTD tail of Rpb1 serves a regulatory role
TFIIE	TFIIEα, TFIIEβ	56 and 34	promoter, TFIIH, Pol II, TFIIF	Recruits TFIIH to the PIC; stimulates enzymatic activities of TFIIH; stabilizes the open DNA conformation
TFIIH	Core domain: XPD, XBP, p62, p52, p44, p34, p8; CAK domain: CDK7, MAT1, cyclin H	~500	downstream DNA, TFIIE, Pol II	CDK7 kinase phosphorylates the CTD; ATP-dependent XPB translocase opens the promoter DNA