1 / 14

Eukaryotic Transcription

Eukaryotic Transcription. Eukaryotic Transcriptional. Transcription control is the most important mode of control in eukaryotes. Three RNA polymerases: RNA Polymerase I: synthesis of pre-rRNA, which is processed into 28S, 5.8S, and 18S rRNAs

meghan
Download Presentation

Eukaryotic Transcription

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Eukaryotic Transcription

  2. Eukaryotic Transcriptional • Transcription control is the most important mode of control in eukaryotes. • Three RNA polymerases: • RNA Polymerase I: synthesis of pre-rRNA, which is processed into 28S, 5.8S, and 18S rRNAs • RNA polymerase III: synthesis of tRNA, 18 S rRNA, and small, stable RNAs • RNA polymerase II: synthesis of mRNAs and four small nuclear RNAs that take part in RNA splicing

  3. Eukaryotic Transcriptional • The main purpose is the execution of precise developmental decisions (irreversible). • Cis-acting control elements are located many kb away from the start site. • Promoter region is poorly characterized.

  4. TATA box About 25-35 bp upstream of the start site +1 5’ TATAAA mRNA start -34 to -26 Well-defined transcription start

  5. Initiator • Instead of a TATA box, some eukaryotic gene contain an alternative promoter element, called an initiator. • Initiator is highly degenerative. +1 5’ Y Y A N T/A Y Y Y Y = pyrimidine (C or T) N = any

  6. CpG island • Genes coding for intermediary metabolism are transcribed at low rates, and do not contain a TATA box or initiator. • Most genes of this type contain a CG-rich stretch of 20-50 nt within ~100 bp upstream of the start site region. • A transcription factor called SP1 recognizes these CG-rich region. • Gives multiple alternative mRNA start sites. mRNA ~100 bp CpG island Multiple 5’-start sites

  7. Enhancers • Located several Kb away from the start site. • Usually ~100-200 bp long, containing multiple 8- to 20-bp control elements. • Cell-type specific • Direction-less (invertible) +1 Enhancer Enhancer

  8. Promoter Proximal Elements • Occur within ~200 bp of the start site. • Contain up to ~20 bp. • Cell-type specific • Invertible +1 Promoter Proximal element

  9. A hypothetic mammalian promoter region Promoter Proximal Element +1 Enhancer Intron Enhancer TATA Enhancer -200 -30 -10~-50 Kb +10~50 Kb Exon

  10. A hypothetic yeast promoter region +1 TATA Enhancer ~-90

  11. mRNA processing Poly (A) site Exon Intron Termination transcription Cap 5’ The 5’-Cap is added to Nascent RNAs (pre-RNAs) shortly after initiation by RNA polymerase II. Pre-mRNAs are associated with hnRNP (heterogeneous ribonucleoprotein particles) proteins containing conserved RNA-binding domains

  12. Poly (A) site Exon Intron Termination Cap 5’ Cap endonuclease 5’ Poly(A) polymerase 5’ A100-250 Pre-mRNAs are cleaved at specific 3’ sites and rapidly polyadenylated

  13. Cleavage and polyadenylation Poly(A) signal Poly(A) site 5’ G/U rich AAUAAA Pre-mRNA 5’ AAAAAA100-250 AAUAAA

  14. Poly (A) site Exon Intron Termination Cap 5’ endonuclease 5’ Poly(A) polymerase 5’ A100-250 RNA splicing 5’ A100-250

More Related