regulation of eukaryotic gene expression Flashcards
stages at which eukaryotic gene expression is regulated
- transcriptional regulation
- mRNA processing
- regulation of mature mRNA
- translation
- post translation
transcription in eukaryotes is same as prokaryotes =
each eukaryotic gene has promotor regions near the start of transcription - 5’ to transcription start site
- promotor sequences and regulatory promotor sequences bind to promotor by RNA polymerase
eukaryotes - what does RNA pol I and III do
transcribes rrNAs, tRNAs, small nuclear RNAs
eukaryotes - what does RNA pol II do
transcribes protein-coding genes and some noncoding RNAs
what is a eukaryotic promotor
DNA sequence that allows initiation and regulation of transcription
-upstream (5’) of transcribed sequence
what does core promotor of eukaryotic promoter contain
binding site for RNA pol II and general transcription factors
-sequences direct RNA pol II to start of transcription
what does regulatory region (proximal control elements) of eukaryotic promoter contain
DNA sequences recognised by regulatory transcription factors - proteins that regulate whether transcription is initiated
what do transcription factors do
bind to eukaryotic promoters, positioning RNA polymerase at the promoter
-helps to separate DNA strands to allow transcription to start
-allows RNA polymerase to leave promoter as transcription starts
-forms a pre-initiation complex needed for transcription to start
what is TATA binding protein (TBP)
general transcription factor
-binds to DNA in minor groove and bends it, so RNA pol can bind to promoter
what transcription factors needed to activate basal level of transcription
CBP and SP1
do transcription factors have the same or different DNA binding domains
different
transcription factors bind to DNA by specific
amino acid side chain : base interactions
what are enhancers
direct bending of DNA and control timing and location of gene transcription
-enhancer sequences about 200 bp long
-can be close to transcription start site or positioned up to 50 kb from start site
-can be positioned upstream or downstream of promoter
-has multiple binding sites for transcription factors
mediator:
complex of proteins that links upstream bound transcription factors to the basal complex
3 regulatory DNA sequences regulate eukaryotic gene transcription
-core promoter region - has TATA box and sequences next to transcription start site
-upstream is proximal control region (regulatory region) that binds regulatory transcription factors
-enhancer sequences which bind regulatory proteins which interact with proteins at the promotor
3 regulatory DNA sequences have cis regulatory sequences - what is this
bound by transcription factors to regulate transcription of genes on the same chromosome as the sequences
3 regulatory DNA sequences have trans regulatory proteins - what is this
RNA pol II and transcription factors bind the trans regulatory proteins, which can bind to their target sequences on any chromosome
how are eukaryotic promotors complex
can have multiple transcription start sites to allow multiple different transcripts to be generated from a single gene
example of tissue specific transcription factors binding to promotor and enchancer sequences leading to tissue specific gene expression
transcription factor MyoD is specific to developing muscle cells
- MyoD binds to E box sequences in the promoters ad enhancers of muscle specific genes
- muscle specific gene expression is activated by MyoD, e.g muscle actin, creatine kinase
cAMP in transcription
many genes in mammals are transcriptionally activated by cAMP
- example of cAMP-responsive gene = PEP carboxykinase catalyses oxaloacetate –> PEP formation in gluconeogenesis
what are histones
small DNA binding proteins coiled around DNA to allow DNA to pack into chromosomes
-high proportion of basic amino acids - lysine and arg
-5 diff histone proteins
histones direct packaging of DNA into nucleosome - what is this
basic subunit of chromatin
-nucleosome (chromatin fibres) form loops which are packed together to form a chromosome
looser packing of chromatin and chromatin remodelling allows
transcription factors to access and bind to DNA
what are open promotors
promotors of constitutively expressed genes (genes expressed in all cells) that are not packed into nucleosomes
- within nucleosome depleted regions (NDR)
- bound by activator proteins (ACT) to allow access for general transcription factors to activate transcription
what are covered promotors
promotors of regulated genes that are packed into nucleosomes
-transcription only happens if the nucleosomes are loosened, displaced or removed
-activator proteins (ACT) and chromatin re-modelling proteins allow unpacking of the chromatin
-allows RNA pol II and transcription factors to bind and activate transcription
chromatin modification by histone acetylation
addition of acetyl groups to specific lysines in the histones reduces +charge so histones bind DNA less tightly
-so loosening of chromatin - RNA pol II and transcription factors to bind DNA
-reversible
how does DNA methylation influence transcription
methylation of cytosine at 5C position to form 5-methylcytosine
-inhibit transcription
-reversible
how many histone proteins are found in a nucleosome
8
sequences useful to search for when looking for protein coding sequences in a genome (3)
poly A addition site
TATA box
CAT box
