mRNA transcription and processing Flashcards
upstream downstream DNA
up: to 5’ of coding strand
down: to 3’ of coding strand
regions on DNA from upstream to downstream
enhancer
promotor
transcription start site (bent arrow) [+1]
transcription terminator site
core promotor vs regulatory promotor
core: consists of the TATA box, where TFs for initiation of transcription bind
regulatory: binds other TFs for enhancing transcription
initiation of transcription (before TFs leave)
1) TATA binding protein (part of TFIID) binds to TATA box, bends DNA
2) TFIIB binds to both TBP and DNA
3) Complex of TFIIF and RNA Pol binds such that RNA Pol is over the transcription start site
4) TFIIE binds, forming a docking site for TFIIH
5) TFIIH binds as 2 subunits with helicase activity, preinitiation complex is formed
6) TFIIH unwinds DNA
initiation of transcription (after TFs leave)
TFs are released, CTD of RNA pol is phosphorylated, allowing RNA pol to move along DNA and do transcription
elongation
RNA pol adds bases 5’-3’, joins together with phosphodiester bonds, separates DNA as it goes
termination
at transcription stop site, polymerase releases completed RNA and dissociates from DNA
5’ capping process
7-methylguanosine added to mRNA through 5’ to 5’ triphosphate linkage
5’ cap function
protection against 5’ to 3’ nuclease digestion
facilitates splicing
facilitates transport from nucleus
translation initiation
role of CTD in mRNA processing
CTD-P binds processing enzymes and factors for capping and splicing of mRNA
where is RNA cleaved for polyedenylation
cleaved at cleavage sites 10 to 30 nucleotides downstream of the consensus sequence (AAUAAA), they are usually located in the untranslated region
cleaved at CA/GU
poly-A tail function and what adds it
added by poly-A polymerase
mRNA nuclear transport, stability, translation
3 sequences required for splicing
splice donor site (AG/GU) at 5’ end of intron
splice acceptor site (AG/G) 3’ end of intron
branch point sequence in intron (A)
lariat formation
5’ end of intron (G) attaches to branch point through phosphodiester bond between 2’ OH of branch A and 5’ P of intron G
removing introns, splicing exons
Spliceosome cleaves 5’ splice donor site then 3’ splice donor site
exons joined via phosphodiester bonds
lariat is cleaved and degraded
alternative splicing defnition and methods
many splicing patterns are tissue specific, the same gene can produce many types of mature mRNA with different exon/3’ UTR structures
- Alternative splicing (splicing out different introns)
- multiple 3’ cleavage sites (last exon length will be different)
