Transcription preinitiation complex

[1][2][3][4] The minimal PIC includes RNA polymerase II and six general transcription factors: TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH.

Archaea have a preinitiation complex resembling that of a minimized Pol II PIC, with a TBP and an Archaeal transcription factor B (TFB, a TFIIB homolog).

An interesting aspect is that the entire complex is bound in an inverse orientation compared to those found in eukaryotic PIC.

[9][10] Formation of the Pol I preinitiation complex requires the binding of selective factor 1 (SL1 or TIF-IB) to the core element of the rDNA promoter.

[14] Pol III has three classes of initiation, which start with different factors recognizing different control elements but all converging on TFIIIB (similar to TFIIB-TBP; consists of TBP/TRF, a TFIIB-related factor, and a B″ unit) recruiting the Pol III preinitiation complex.

Cluster of ovals representing the transcription preinitiation complex is sandwiched inside a curved strand of DNA, between the promoter region on one end and the enhancer region on the other.
Transcription preinitiation complex, represented by the central cluster of proteins, causes RNA polymerase to bind to target DNA site. The PIC is able to bind both the promoter sequence near the gene to be transcribed and an enhancer sequence in a different part of the genome, allowing enhancer sequences to regulate a gene distant from it.