Transcription Flashcards
DNA-dependent synthesis of RNA
transcription
template of transcription
DNA (anti-coding/antisense strand)
product of transcription
- messenger RNA (mRNA)
- ribosomal RNA (rRNA)
- transfer RNA (tRNA)
- miRNA, siRNA, and other regulatory RNAs
- more on regulation
- degrades mRNA
- ribonuclease action
- delay translation
microRNA (miRNA)
able to regulate the expression of genes, by a phenomenon known as RNAi (RNA interference)
siRNA (small interfering RNA)
DNA sequences that code for RNA
coding regions
do not code for an RNA
noncoding regions
3 general steps of transcription
- initiation
- elongation
- termination
major point of control of gene expression
initiation
main enzyme for transcription
RNA Polymerase
basic unit of a gene which extends from promoter to terminator
transcription unit
immediate product of RNA polymerase before any changes occur to the RNA
primary transcript/ pre mRNA/ heterogenous nuclear RNA (hnRNA)
regions close to promoter
proximal
regions farther away from promoter
distal
base pair of DNA which corresponds to the first RNA nucleotide added by RNA polymerase
start point
DNA sequence from startpoint to any nucleotides located towards the direction of transcription
downstream sequences (+)
DNA sequence from startpoint to any nucleotide(s) located opposite/away from the direction of transcription
upstream sequences (-)
nucleotide sequence which when aligned with each other have certain nucleotides that at certain positions occur at high frequency
consensus
- DNA-directed
- adds ribonucleotide units to the 3”OH end of the RNA chain
- no proofreading ability
RNA Polymerase
RNA polymerase builds RNA in the __ direction
5’ - 3’
core enzyme of RNA polymerase
2αββ’
holoenzyme of RNA polymerase
(2αββ’)σ
subunit of RNA polymerase
- 2α
- β
- β’
- σ
- ω
aids in promoter recognition
2α
gene of 2α
rpoA
binds ribonucleotide substrate
β
gene of β
rpoC
binds DNA template
β’
gene of β’
rpoB
recognizes and binds tightly to promoter
σ
gene of σ
rpoD
facilitate assembly
ω
- binds to β subunit of bacterial RNA pol
- prevents initation of transcription
rifampicin
where does rifampicin bidn to
β subunit of bacterial RNA pol
what does rifampicin prevent
initation of transcription
types of eukaryotic RNA polymerases
- I
- II
- III
RNA pol I: location
nucleolus
RNA pol I: no. / cell
40, 000
RNA pol I: genes transcribed
rRNA
RNA pol I: % activity
50-70%
RNA pol II: location
nucleoplasm
RNA pol II: no. / cell
40,000
RNA pol II: genes transcribed
hnRNA (precursor of mRNA)
RNA pol II: % activity
20-40%
RNA pol III: location
nucleoplasm
RNA pol III: no. / cell
10, 000
RNA pol III: genes transcribed
- tRNA
- 5s rRNA (small stable RNAs)
RNA pol III: % activity
0.1
Six sites of activity of RNA polymerase
- DNA coding strand
- DNA template strand
- RNA binding
- RNA-DNA hybrid
- Unwinding point
- Rewinding point
antisense/ anticoding/ minus (-) strand
DNA template strand
- sense/coding/plus (+) strand
- DNA strand complementary to the template
- identical in sequence with RNA transcribed (U instead of T)
noncoding strand
noncoding strand is a DNA strand __ to the template
complementary
- specific sequences that are required for initiation
- promotes gene expression
promoter/s
several proteins that interact with RNA pol
transcription factors (TFs)
what is required in the initation of transcription
- promoter/s
- transcription factors
promoters are binding site of what?
RNA polymerase
Prokaryotic Promoters
- Pribnow box/ -10 sequence
- -35 sequence
who discovered the Pribnow box
David Pribnow
consensus sequence of the Pribnow box
TATAAT
where is the -35 sequence found
upstream from Pribnow box
consensus sequence of -35 sequence
TTGACA
- one for each type of RNA polymerase
- because there is a specific RNA polymerase for each type of RNA
eukaryotic promoters
promoter for RNA pol I
bipartite (core + UCE)
promoter for RNA pol III
located within the gene it promotes
Eukaryotic promoters: general structure
- TATA box or Goldberg-Hogness box
- CCAAT box
- GC box
TATA box or Goldberg-Hogness box
- TATAWAW
- 19-27 bases before startpoint
W in TATAWAW
Adenine or Thymine
CCAAT box
~70 bases before startpoint
GC box
~40 bases before startpoint
Roles of Eukaryotic Promoters
- AT rich region makes initial unwiding easier
- orientation of RNA polymerase relative to startpoint
- binding of auxillary proteins to facilitate RNA polymerase binding
auxillary protiens
transcription factors
Two types of promoter
- strong promoter
- weak promoter
- same as consensus sequence
- RNA pol binds strongly
- initiation - more frequent
- more transcripts made
strong promoter
- deviates significantly from consensus sequence
- RNA pol binds weakly
- initiation - less frequent
- less RNA transcript made
weak promoter
Two types of promoter mutation
- down mutation
- up mutation
causes deviation from consensus sequence
down mutation
example of down mutation
TATAAT -> TAGCAT
causes a given sequence to become more/exactly similar to an established consensus sequence
up mutation
example of up mutation
TATGTT (lac operon) -> TATATT
- protein factors
- essential for transcription initiation of any eukaryotic gene
- sufficient to direct basal/genneral level of transcription from many core promoters
- position RNA polymerase at the promoter and send it on its way
general transcription factors
where are general transcription factors essential for
transcription initiation
general transcription factors are sufficient to direct what?
basal/general level of transcription
where do general transcription factors position RNA polymerase
promoter
where phosphorylation happens
alpha CTD
- proteins involved in inclusive interaction and selective activation of particular genes or groups of genes
- different sets in different cell types -> different patters of gene expression
gene-specific transcription factors
where are gene-specific transcription factors involved in
inclusive and selective activation of particular genes
different sets in different cell types -> ?
different patters of gene expression
example of gene-specific transcription factors
- steroid hormone receptor
- myogenic proteins
activtes glucocorticoid response element
steroid hormone receptor
activates genes for muscle differentiation
myogenic proteins
what happens to the RNA polymerase during transcription initiation
- binds promoter
- melts DNA
- remains stationary
- incorporates the 1st ribonucleotide - retails all 3 phosphate groups
amount of nucleotides in elongation of transcription
50 nucleotides / sec
direction of transcription
5’-3’ wrt RNA product
end which unwinds the DNA
leading end
end which rejoin the DNA
tailing end
- intercalates DNA
- prevents movement of RNA pol
- inhibits elongation
- actinomycin D
- acridine
what do the actinomycin D and acridine inhibit
elongation
what does the acridine specifically inhibit
topoisomerase II
signals RNA pol to stop
termination sequence
what happens during termination
- RNA transcript released
- RNA polymerase detaches
Two types of Termination
- Rho-independent
- Rho-dependent
- simple termination
- no need for rho factor
- ends in a stretch of AAAAAAA (DNA), UUUUUUU (RNA)
- palindrome rich in GC
- mRNA forms a hairpin
rho-independent termination
what is formed in rho-independent termination
hairpin
termination: __ rich in GC
palindrome
- requires rho factor
- palindrome: less GC-rich
- no UUUUU at end of RNA
rho-dependent termination
where does the rho bind to transcript
rut site (rho utilization site)
releases transcript during rho-dependent termination
rho helicase
what happens after the rho catches up to the RNA polymerase that is paused at terminator
rho unwinds DNA-RNA hybrid