RNA Polymerase II Holoenzyme and Transcription Factors

Abstract The transcription, which is the RNA ( ribonucleic acid ) biosynthesis, constitutes a tightly regulated multistep process involving the spatial and temporal recruitment of numerous protein complexes. The three main steps of the process are transcription initiation with the formation of the transcription preinitiation complex (PIC), elongation and termination. All these steps have in common the enzymatic activity of the protein complex known as the RNA polymerase II (RNAPII), which is an enzyme giving rise to the promoter‐specific protein complex called RNAPII holoenzyme. The composition of RNAPII holoenzyme (dependent on the extraction/purification process and the origin of the material) varies from laboratory to laboratory, but always includes RNAPII, general transcription factors (GTFs), protein mediators such as the suppressor of RNA polymerase B mutations (SRBs), histone acethyl transferase (HAT) and chromatin remodelling factors. This article focuses on the structure of RNAPII and the protein complex leading to the formation of RNAPII holoenzyme during the initiation step. The role of the main proteins allowing specific promoter recognition is detailed. Key concepts: The transcription is a regulated multistep process (initiation, elongation and termination) leading to RNA synthesis. RNA polymerase synthesizes RNA in a DNA‐dependent manner. Six RNA polymerases are known in eukaryote: RNAPI (synthesizing rRNAs), RNAPII (synthesizing mRNAs and snRNAs), RNAPIII (synthesizing tRNAs, 5S rRNA and some snRNAs), spRNAP‐IV (synthesizing mRNAs) and RNAP IV (synthesizing siRNA). Transcription requires cis ‐acting promoter elements (core and regulatory elements) and trans ‐acting factors. The core elements bind the transcription preinitiation complex (PIC) that include the GTFs (general transcription factor) and RNAPII. Two main forms of RNAPII holoenzyme are identified, the SRB/MED‐containing and the PAF complex‐containing holoenzyme.