Structural Components
The clamp swings to trap the DNA in the cleft. Further along, the wall sends the DNA template through the cleft in approximately a 90° turn. Both the clamp and wall are parts of the Rpb2 subunit. Further along in the process, the rudder separates the newly synthesized RNA strand from the DNA template. The DNA reforms into a double helix as it leaves RNA pol II.
Other components of RNA pol II include the following:
The jaw is the opening through which DNA enters. The funnel is what the NTP’s travel through to be incorporated into the growing RNA strand, and the pore is the end of the funnel. The bridge is an Rpb1 segment that translocates the DNA-RNA combination at the end of each cycle of catalysis. Magnesium is located within the active site and functions as the catalyst.
Mechanism of Action
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Alpha Amanitin
α-Amanitin is a bicyclic octapeptide that adheres tightly with RNAP II, which blocks the elongation steps. α-amanitin binds in the funnel and interacts with the bridge helix and adjacent Rpb1, but it does not inhibit the RNA pol II’s interaction with NTP. Instead, α-amanitin likely challenges the bridge’s conformational change that is necessary for the purposed RNAP translocation step. α-Amanitin, found in the poisonous mushroom death cap, leads to death after several days. This time frame aligns with the rate at which mRNA’s and proteins turnover.
Modifications
General Transcription Factors
In both eukaryotes and prokaryotes, the basic mechanism for initiating transcription is the same: protein factors selectively bind to promoter regions on DNA. Prokaryotes use sigma factors while eukaryotes use a complex of 6 general transcription factors (GTFs). These GTFs are all named similarly and begin with TF, for transcription factor, followed by the Roman numeral II since they are involved in transcription by RNAP II. The combination of all the transcription factors bound to the DNA promoter region, in complex with RNAP II, is called the preinitiation complex (PIC). The formation of the PIC occurs in an ordered pathway, beginning with the TATA box which is a promoter region on DNA at position -27.
Process of PIC formation:
1. TFIID contains a subunit named the TATA binding protein (TBP), which recognizes and binds to the TATA box on the dna promoter
TFIID/TBP
TFIIB
TFIIA
TFIIF
TFIIE
TFIIH
Yan, C., Dodd, T., He, Y., Tainer, J. A., Tsutakawa, S. E., & Ivanov, I. (2019). Transcription preinitiation complex structure and dynamics provide insight into genetic diseases. Nature Structural and Molecular Biology, 26(6), 397-406. https://doi.org/10.1038/s41594-019-0220-3
