General Transcription Factors

In eukaryotic cells, transcription initiation by RNA polymerase II requires at least six different general transcription factors — TFIIA, IIB  , IID, IIE, IIF, and IIH.

These proteins bind to gene promoter regions along with RNA polymerase and regulate the gene expression. 

TFIID is a multiprotein complex containing a TATA-binding protein or TBP subunit, which binds to the TATA box region found in most promoters. 

Next, TFIIA and TFIIB attach to the TFIID-DNA complex. TFIIA stabilizes the TFIID-DNA complex, while TFIIB positions the preformed polymerase-TFIIF complex at the transcription start site.

TFIIF facilitates and stabilizes the interaction of RNA polymerase II with the other transcription factors.

TFIIE is then tethered to the DNA, which further recruits TFIIH. The DNA helicase subunit of TFIIH unwinds the double-stranded DNA.

The sequential binding of the general transcription factors and RNA polymerase II at the promoter results in the formation of the transcription pre-initiation complex.