Biochemistry and Molecular Biology II – Lecture 2: Transcriptional control of
gene expression #1
17-04-2018
Transcription can be divided in three steps:
1. Initiation
2. Elongation
3. Termination
- Transcription starts at the promoter region which contains the promoter
sequence.
- Transcription stops at the terminator region which contains the terminator
sequence.
RNA polymerase recognizes these specific promoter and terminator sequences.
Promoter recognition in prokaryotes:
The sigma-factor (small part of RNA-polymerase) defines:
1. Starting point
2. Direction
3. Intensity
Of transcriptional initiation.
The sigma factor is a key characteristic for prokaryotic promoter recognition.
The sigma factor recognizes the specific -10 sequence (TATA-box) and -35
sequence (ACAGTT-sequence).
Different genes are expressed at different levels, due to repressor proteins.
- There is only one RNA-polymerase in prokaryotes, but there are multiple
sigma factors.
o Sigma-factor 70 is the main sigma factor, which acts as a
housekeeping gene.
o Stationary phase genes in bacteria are activated by the presence of
Sigma-factor S.
Different sigma factors recognize different promoter sequences.
, The lac operon:
Common regulation for enzymes required for lactose metabolism.
Lactose is converted into glucose and galactose by B-galactosidase.
Polycistronic mRNA encodes for three proteins at once:
1. B-galactosidase
2. Lactose permease
gene expression #1
17-04-2018
Transcription can be divided in three steps:
1. Initiation
2. Elongation
3. Termination
- Transcription starts at the promoter region which contains the promoter
sequence.
- Transcription stops at the terminator region which contains the terminator
sequence.
RNA polymerase recognizes these specific promoter and terminator sequences.
Promoter recognition in prokaryotes:
The sigma-factor (small part of RNA-polymerase) defines:
1. Starting point
2. Direction
3. Intensity
Of transcriptional initiation.
The sigma factor is a key characteristic for prokaryotic promoter recognition.
The sigma factor recognizes the specific -10 sequence (TATA-box) and -35
sequence (ACAGTT-sequence).
Different genes are expressed at different levels, due to repressor proteins.
- There is only one RNA-polymerase in prokaryotes, but there are multiple
sigma factors.
o Sigma-factor 70 is the main sigma factor, which acts as a
housekeeping gene.
o Stationary phase genes in bacteria are activated by the presence of
Sigma-factor S.
Different sigma factors recognize different promoter sequences.
, The lac operon:
Common regulation for enzymes required for lactose metabolism.
Lactose is converted into glucose and galactose by B-galactosidase.
Polycistronic mRNA encodes for three proteins at once:
1. B-galactosidase
2. Lactose permease
