lec 9 Flashcards
(14 cards)
initiation involves stabilization of transcription initiation complex
once stabilized
- RNA Pol II = released by complex to start elongation
epigenetic mechanisms affect gene expression without changing underlying DNA seq
- DNA methylation
- chromatin structure
RNA Pol II complex
- critical for transcription of pre-mRNA/nRNA
- large complex protein that moves stepwise along DNA to unwind helix
- adds nucleotides to make new nRNA copy of DNA template
- associates with proteins that process nRNA
stability of transcription initiation complex refers to
how well TFs bind to DNA and recruit RNA Pol II
- determines how many molecules of RNA Pol II will be recruited
- determines how many transcripts are generated
- determined by how strong binding is between enhancers and TSTFs
> > stable transcription initiation complex
> > RNA Pol II recruited
-»_space; mRNA transcripts made
=»_space; transcription efficiency
enhancers
DNA seq that binds to TSTFs and can reside in UTRS or introns
- TSTFs to enhancer binding controls time, place, and efficiency of transcription
- many enhancers bind to many enhancer regions
- many genes have many enhancer regions
> will turn on transcription in different tissues in response to TSTFs
enhancer mechanism
bind to TFs that
1. recruit modifying enzymes
- histone acetyltransferases
2. stabilize transcription initiation complex
reporter genes and study of enhancers
reporter genes
- detect/measure the level of gene expression driven by regulatory regions
- indicate when, where and how much a gene is normally expressed
constructs allow visualization of gene expression controlled by regulatory regions (e.g. enhancers)
DNA mod can affect transcription
DNA methylation inhibits transcription
- on cytosine nucleotides
- alters gene expression as cells differentiate
- prevents binding of TFs
- recruiting histone mod enzymes (histone de-acetylases)
> lead to condensed, repressed chromatin
- form of epigenetic memory
DNA methylation of cytosine residue vs. methylation of amino acids of histone tails
DNA methylation always lead to transcriptional repression
histone methylation can lead to
transcriptional activation and repression
CpG islands
- many CpG sites in CpG islands of promoters cause stable silencing of genes
- DNA methylation regions in promoters known to regulate gene expression through transcriptional silencing of corresponding gene
DNA methyltransferases
important in modifying DNA
1. Dnmt 3
- performs initial methylation of cytosine
- de novo
- active during early stages of embryonic development
2. Dnmt 1
- ensures that methylation pattern is perpetuated every time DNA is replicated
- perpetuating
- active during cell cycle
> to preserve methylation in daughter cells
> recognizes hemimethylated DNA and methylates C’s on other strand
do all mitotic descendants maintain the same methylation pattern?
Yes
