Why does RNA pol II pause?
RNA polymerase II (Pol II) pauses downstream of the transcription initiation site before beginning productive elongation. This pause is a key component of metazoan gene expression regulation. Some promoters have a strong disposition for Pol II pausing and often mediate faster, more synchronous changes in expression.
How does RNA pol II stop?
Three mechanisms are proposed to cause Pol II termination: conformational changes induced by binding of factors to Pol II; collision of an exoribonuclease with Pol II; and/or disruption of the Pol II active site hybrid by an RNA–DNA helicase.
Does RNA polymerase 2 have proofreading ability?
This proofreading mechanism enables Pol II to cleave the dinucleotide containing a mismatched 3′-RNA terminus through backtracking-dependent proofreading mechanism to regenerate a new post-translocation state, allowing Pol II to have a “second chance” to reselect the correct nucleotide for incorporation and elongation.
What are the important features of CTD of RNA polymerase II?
The C-terminal repeat domain (CTD), an unusual extension appended to the C terminus of the largest subunit of RNA polymerase II, serves as a flexible binding scaffold for numerous nuclear factors; which factors bind is determined by the phosphorylation patterns on the CTD repeats.
What causes termination of translation?
Translation termination occurs when the ribosome encounters a stop codon (UAG, UAA, or UGA) in the A site. Stop codons in bacteria are recognized by RF1 and RF2: RF1 recognizes UAG and UAA codons, whereas RF2 recognizes UGA and UAA.
What causes transcription termination?
Transcription termination is caused by the destabilization and/or a conformational change of the Pol II EC after transcribing the poly(A) site. Release of antitermination factors (left) or recruitment of termination factors (right) triggers dissociation from template DNA.
Why RNA polymerase has no proofreading?
It is generally assumed that RNA pol. does not need to proofread, because RNA molecules are working copies that can tolerate a few errors (and can be replaced by new copies transcribed from the DNA).
Which proofreading activities are performed by RNA polymerase?
Proofreading begins with fraying of the misincorporated nucleotide away from the DNA template, which pauses transcription. Subsequent backtracking of RNAP by one position enables nucleolytic cleavage of an RNA dinucleotide that contains the misincorporated nucleotide.
What is the role of CTD?
The CTD functions to help couple transcription and processing of the nascent RNA and also plays roles in transcription elongation and termination.
What is CTD code?
A series of different phosphorylations and conformation changes generates configurations specific for binding of particular factors. In essence, there is a CTD ‘code’ that specifies the position of RNAPII in the transcription cycle. The two major CTD phosphorylations occur at distinct points in the transcription cycle.