Transcription factor

In gene expression, the transcription of DNA to RNA is controlled by proteins called transcription factors. In eukaryotes there are 6 general transcription factors (GTFs): TFIIA, TFIIB, TFIID, TFIIE, TFIIF and TFIIH, each of which have a different role in regulating gene transcription. All GTFs are multi-subunit, except for TFIIB.

The GTFs are involved in the preinitiation complex (PIC)  assembly which positions RNA polymerase II and separates the template strand at the transcription start site through a number of steps as outlined:

1. TFIIA facilitates and stabilises TFIID binding to the TATA box.

2. TFIID recruits the single subunit factor TFIIB.

3. With this interaction, TFIIB recruits RNA polymerase II-TFIIF complex (TFIIF is joined to RNA polymerase II prior to this recruitment.)

4. The recruitment of the RNA polymerase II-TFIIF allows TFIIE and then finally TFIIH to bind, completing the PIC assembly.

This is known as the classical pathway, not all promoters are turned on in this way.