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EUKARYOTIC TRANSCRIPTION, EUKARYOTIC RNA POLYMERASES - Coggle Diagram
EUKARYOTIC TRANSCRIPTION
EUKARYOTIC RNA POLYMERASES
RNA polymerase I
CLASS I TRANSCRIPTION UNIT
Contains genes coding for:
18S rRNA
5.8S rRNA
28S rRNA
Genes are arranged in tandem repeats
Individual transcription units are separated
by non-transcribed spacer regions
RNA Pol I transcribes the rRNA genesRNA Pol I transcribes the rRNA genes
Pre-rRNA is produced
Pre-rRNA undergoes processing
↓
Mature rRNA products are formed
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PROMOTER RECOGNITION
RNA Pol I requires specific promoter elements
for recognition and initiation
Bipartite promoter
Upstream Control Element (UCE)
Located from −187 to −107
Helps regulate promoter activity
Promoter elements are recognized by
transcription factors
Proceed to transcription complex formation
Core promoter
Located from −31 to +6
Required for transcription initiation
RNA ELONGATION
RNA Pol I moves along the DNA template
Complementary ribonucleotides are added
to the growing RNA chain
RNA is synthesized in the 5′ → 3′ direction
The RNA transcript becomes longer
A complete pre-rRNA transcript is produced
FORMATION OF TRANSCRIPTION COMPLEX
UBF1 (Upstream Binding Factor 1)
Binds to the UCE and core promoter
RNA Pol I begins joining ribonucleotides
Helps organize the promoter region
SL1 (Selectivity Factor 1) is recruited
SL1 binds to UBF1
UBF1 and SL1 help assemble the
transcription initiation complex
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RNA PROCESSING
Newly synthesized pre-rRNA undergoes processing
Pre-rRNA is processed into mature rRNAs
18S rRNA
5.8S rRNA
28S rRNA
Mature rRNAs participate in ribosome formation
Functional ribosomal subunits are produced
TRANSCRIPTION INITIATION
RNA Pol I binds at the core promoter
RNA Pol I begins joining ribonucleotides
Phosphodiester bonds form between
successive ribonucleotides
RNA chain begins to grow
Pre-rRNA synthesis starts
RNA polymerase II
PROMOTER RECOGNITION :TFIID binds promoter through TBP and TAFs
TFIIA stabilizes TBP–DNA binding
RNA Pol II–TFIIF joins
TFIIE joins
TFIIH joins
PRE-INITIATION COMPLEX FORMED
Template strand exposed
Complementary NTPs bind
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ELONGATION +TERMINATION
RNA Pol II clears the promoter
TFIIH phosphorylates RNA Pol II CTD
RNA synthesized 5′ → 3′
RNA Pol II moves along DNA
CTD phosphorylation recruits
RNA-processing factors
5′ capping and splicing enzymes recruited
Pre-mRNA continues to elongate
AAUAAA polyadenylation signal recognized
RNA transcript is cleaved
Cleavage occurs about 15–30 nucleotides downstream
Poly(A) polymerase adds AMP residues
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RNA polymerase III :
Transcribes small non-coding RNAs
Main products → tRNA, 5S rRNA and other small RNAs
Promoter recognition
Internal promoter elements are recognizedInternal promoter elements are recognized
RNA Polymerase III binds to the promoter
Transcription initiation
DNA is unwound and RNA synthesis begins
RNA Polymerase III moves along the DNA template
and adds complementary ribonucleotides
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