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Lecture 9

BIO130H1 Lecture Notes - Lecture 9: Non-Coding Rna, Messenger Rna, Sigma Factor

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Kenneth Yip

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LECTURE 9 & 10
Transcription II
Simplified Model of Gene Expression
More Realistic Model
o Polycistronic mRNA generating multiple proteins
o Usually product of a single promoter to coordinate expression
o Makes sense for bacteria because allows them to use single promotor with single
type of sigma factor to coordinate genes all at once
Cell might be in environment with lots of sugars
Need set type of proteins
Quick way to regulate gene expression
Eukaryotic Transcription is More Complicated
o Need to cleave end and add poly A-tail
o Introns sequences removed before we make final messenger RNA
Gene Structure
o The non-coding sequence is NOT an intron

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o SnRNA, snoRNA and scaRNA process other RNAs
o miRNA and siRNA important for gene regulation
o non-coding RNA associated with telomerase (RNA template in telomerase)
Number of Eukaryotic RNA Polymerases Required
o Each of these RNAPs is a multi-subunit protein
o Each is responsible for transcription of different RNAs
o Since we need to make so many types of RNA, good to have division of labor

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Subunits of Eukaryotic RNA Polymerases
o RNAP’s are complex structures with many subunits
Some subunits are common to all three RNAPs
Some subunits resemble the subunits of bacterial RNAPs
o 5 subunits
o Carboxyl terminal domain (CTD)
A tail of amino acids that extend out of B’ subunit
Eukaryotic vs Bacterial RNA Polymerases
o Eukaryotic RNA polymerases require proteins to help position them at the
promoter called transcription factors
Separate entities
o These factors fulfill a similar role to the sigma subunit of bacterial RNA
o Eukaryotic NA polymerases need to deal with chromosomal structures
Prokaryotic and eukaryotic packaging slightly similar, but eukaryotic takes
it to new level
More protein needed to need deal with packaging (chromosome
o Eukaryotic promoter sequences do NOT always contain a TATA box sequence
o TBP (TATA binding sequence) binds in minor groove
Bends helix at TATA box sequence
Acts as flag for other transcription factors to assemble
o Some promotor sequences transcribed in eukaryotes
Steps in the Initiation of Transcription
o Binding of TBP along with rest of TFIID (includes
o Mobilizes the binding of TFIIB complex adjacent to
TATA box
o RNAP can now bind in correct orientation at start site
Want it to transcribe at +1
o Other transcription factors associate at this location
o TFIIH has special properties
Has helicase domain (open up helix)
Has kinase domain (can put phosphate groups
on proteins; changes activity)
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