CSB349H1 Lecture Notes - Lecture 5: Ribonuclease, Polyadenylation, Guanine
14 May 2018
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Lecture 5(c): Transcription III
Divergent Transcription – Twist #1:
• Active promotors can have transcription occurring in the opposite directions
o Giving rise to anti-sense transcripts
§ This can be seen when sequencing for RNAs
Initiation Occurs in Inactive Genes – Twist #2:
• RNAPII is found binding to the TSS even when a gene is inactive
o Both types of genes (actively transcribed and inactive)
display having methylated H3K4
ð Therefore, inactive genes display initiation of transcription; however there is no expression
ð Problematic; if PIC is the ‘rate limit step’ in transcription – we see inactive genes have the
PIC but are not expressed?
o This suggests that there must be other regulators of transcription and not just the PIC
Promotor Escape:
• Once the PIC is formed and everything is set it will give ‘clearance’
to the RNAPII
o RNAPII will begin transcribing; in the initial stages (few bp),
RNAPII will undergo a behavioral change and
escape the promotor
§ Only once the RNAPII escapes the promotor will
it be committed to transcribing the entire RNA
Elongation:
• Once the RNAPII has initiated transcription it shifts into an
elongation phase
o Shift is involved in dissociating majority of the TFs and
Mediator – will be replaced by TFIIS and Spt5
§ Known as elongation factors which regulate elongation
RNA Processing:
• There are 3 main RNA processing
steps dependent on the CTD
a. 5’-capping
b. Splicing
c. Polyadenylation & Cleavage
ð CTD stimulates the recruitment of factors responsible for these processes in individual events
• During elongation:
o Fcp1 (phosphatase) will remove the phosphate on Serine 5 to remove capping factors
o P-TEFb (kinase) will phosphorylate Serine 2 to recruit splicing & polyadenylation
factors
Document Summary
Lecture 5(c): transcription iii: active promotors can have transcription occurring in the opposite directions, giving rise to anti-sense transcripts. This can be seen when sequencing for rnas. Initiation occurs in inactive genes twist #2: rnapii is found binding to the tss even when a gene is inactive, both types of genes (actively transcribed and inactive) display having methylated h3k4. Therefore, inactive genes display initiation of transcription; however there is no expression. Problematic; if pic is the rate limit step" in transcription we see inactive genes have the. Pic but are not expressed: this suggests that there must be other regulators of transcription and not just the pic. Promotor escape: once the pic is formed and everything is set it will give clearance" to the rnapii, rnapii will begin transcribing; in the initial stages (few bp), Rnapii will undergo a behavioral change and escape the promotor.
