General transcription factor

General transcription factors (GTF's) or basal transcription factors are protein transcription factors that have been shown to be important in the transcription of class II genes to mRNA templates. Many of them are involved in the formation of a preinitiation complex, which, together with RNA polymerase II, bind to and read the single-stranded DNA gene template.

Functions
GTFs are intimately involved in the process of gene regulation, and most are required for life. TATA binding protein, (TBP) is a GTF that binds to the TATAA box (T=Thymine, A=Adenine) the motif of nucleic acids that is directly upstream from the coding region in all genes. TBP is responsible for the recruitment of the RNA Pol II holoenzyme, the final event in transcription initiation. These proteins are ubiquitous and interact with the core promoter region of DNA, which contains the transcription start site(s) of all class II genes.

Not all GTFs play a role in transcriptional initiation; some are required for the second general step in transcription, elongation. For example, members of the FACT complex (Spt16/Pob3 in S. cerevisiae, SUPT16H/SSRP1 in humans) facilitate the rapid movement of RNA Pol II over the encoding region of genes. This is accomplished by moving the histone octamer out of the way of an active polymerase and thereby decondensing the chromatin.

Types
The general transcription factors that are required for transcription by RNA polymerase II in vitro are :
 * TFIIA (see TFIIA; TFIIA is not a real basal transcription factor.)
 * TFIIB (see TFIIB)
 * TFIID (see TFIID and TATA binding protein)
 * TFIIE (see TFIIE)
 * TFIIF (see TFIIF)
 * TFIIH (see TFIIH)

Note: Basal transcription in test tubes has been achieved using only highly-purified recombinant TFIIB and TFIIF.