lec 7.3 - RNA pol II

RNA polymerase II - structure

• has CTD portion - carboxyl tail domain

specific functions of CTD

• transcription initiation - recruits transcription factors to promoter region of genes

• capping RNA transcripts - addition of 5' cap to nascent mRNA molecules for mRNA stability

• attaching to spliceosome - spliceosome removes introns and joins exons in pre-mRNA

composition of CTD

• multiple repeats of 7 AAs: Tyr-Ser-Pro-Thr-Ser-Pro-Ser

  • easily phosphorylated and can bind other proteins for regulation, RNA splicing, or capping

what RNA pol II transcribes and elements involved in its transcription

• transcribes most structural genes (mRNAs) and miRNAs (micro RNA)

• involves promoter seq

  • contains several short-sequence (~10 bp) elements that bind transcription factors, dispersed over ~100 bp

• involves enhancer seq

  • contains a more closely packed array of elements that also bind transcription factors

  • is located several hundred bp to several kilo-bases away from transcription start site

transcription start site name and describe the 2 types of 2 promoters

• 2 types of core promoters

  1. Inr (initiator) + TATA

     • Inr has pyrimidines (Y) surrounding the CA at the start point (Py2CAPy5)

     • a minimal pol II promoter may have a TATA box ~25 bp upstream of the Inr

       • TATA box has the consensus sequence of TATAA

  2. Inr + DPE (downstream promoter element)

     • the DPE is downstream of the start point

which part of RNA pol II recognizes promoter?

• requires transcription factors instead of sigma factor

  • TBP - (tata-binding protein) required by all three pol

  • TFIID - protein complex that includes TBP

  • TFIIB and TFIIC - transcription factors

  • TFIIF - binds to RNA pol

  • TFIIH - phosphorylates CTD of RNA pol

  • TFIIE

TBP – universal factor

• where does it bind?

• what does it do?

• binds to minor groove and causes DNA to bend by 80º

• allows transcriptional factors and RNA polymerase to form a closer association with DNA

  • opens up DNA more to get better binding

summary of RNA pol II and transcription

• an initiation complex assembles at promoters for RNA pol II by an ordered sequence of association with transcription factors

  • TFIID consists of TBP plus its associated TAFs (TBP-associated factors)

  • TFIIB, TFIIE and TFIIH needed to melt DNA

  • phosphorylation of CTD required for promoter clearance