19: Eukaryotic transcription Flashcards
How is there spatial separation in eukaryotes in eukaryotic transcription?
nucleus - DNA rep and transcription
cytoplasm - translation
bacteria - transcription and translation occur simultaneously
What are potential points in the regulation of gene expression in eukaryotes? How do they compare with prokaryotes?
- transcriptional control (both)
- RNA processing (euk.)
- RNA transport/localization (euk.)
- mRNA degradation control (both)
- translation control (both)
- inactivate nMRA for storing and later use (euk)
- protein activity control (mostly euk)
What enzyme is active in eukaryotic transcription?
RNA Polymerase II makes mRNA
1 makes rRNA
3 makes tRNA
What are the important enzymes/factors for eukaryotic transcription initiation?
- RNA poly 2
- 5 general transcription factors (GTFs) - one binds to TATA box
- multi-subunit complex called Mediator
What is a distinction for eukaryotic and bacterial transcription initiation?
euk GTFs are equivalent to sigma factor in bacteria: they recognize and bind promoter elements to recruit RNA poly II
What is a distinction between eukaryotic and bacterial termination?
bacteria: Rho dependent termination possibility
eukaryotes: termination involves nucleotide sequence that can be modified for poly A tail
What are transcription activators and repressors?
activator: binds to enhancer elements that can be distant from TATA element
repressor: binds to silencer elements
What are the differences between eukaryotic and prokaryotic RNA polymerase?
bacteria: single RNA polymerase with 2 a, 1B, and 1B’ subunits
eukaryotes: 3 types of RNAP
What is a distinction in the promoter region for eukaryotes and bacteria?
- no operon in eukaryotes, each gene is transcribed as a single unit
(bacteria is polycistronic and eukaryotes are monocistronic)
- Eukaryotic promoters do not have -10 and -35 sequences - there is no sigma factor - but does have TATA box
What are the elements of a eukaryotic promoter?
- Transcription factor B2 recognition element
- TATA box
- Initiator sequence
- Motif 10 element (regulatory)
- Downstream promoter element
What are the steps of initiation in eukaryotic transcription?
- TATA binding protein (part of TF2D) binds to TATA box
- other transcription factors assemble with RNA poly = preinitation complex
- pre initiation complex binds to DNA
- at the same time, activator binds to enhancer site upstream of promoter region
- mediator protein (not bound to DNA but is bound to RNA polymerase) binds in the middle of DNA looped back structure
- when mediator is bound to activator protein (which is bound to enhancer site) conformational change = transcription induced
What are transcriptional control differences in bacteria vs eukaryotes?
- eukaryotes can have regulatory proteins bind to DNA several thousand base pairs away or even on difference chromosomes from start site bc mediator will bind to them eventually
- mediator takes info from regulator proteins and relay info to RNA poly (combinational control)
- more range of expression due to mediator control
What is the difference between eukaryotes and prokaryotes in DNA accessibility?
DNA is always available to transcribe in bacteria
chromosome/nucleosome structure, large genome and histone association makes DNA less accessible bc it physically blocks RNA polymerase
What are the two factors that allow for DNA to be accessible in eukaryotes?
How do these factors work?
- chromatin-remodelling complexes
- Histone-modifying enzymes
(unwinds DNA by pulling strand out, but not off, of histone, exposing the promoter) - transcription activation
How do chromatin-remodelling complexes work?
regulatory transcription factors recruit chromatin remodelling complexes and through ATP dependence, conformational change occurs in nucleosome structure so that promoter is exposed and can be transcribed
