BIO130H1 Lecture Notes - Lecture 9: Non-Coding Rna, Messenger Rna, Sigma Factor
BIO130
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
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
→ 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
polymerases
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
structures)
→ Promoters
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
TAFs)
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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BIO130H1 Full Course Notes
Verified Note
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