prokaryotic transcription and factors responsible

1. The synthesis of RNA molecules using DNA strands as
the templates so that the genetic information can be
transferred from DNA to RNA.
Transcription

2. • The whole genome of DNA needs to be replicated, but
only small portion of genome is transcribed in
response to the development requirement,
physiological need and environmental changes.
• DNA regions that can be transcribed into RNA are
called structural genes.

3. Transcriptional Control
DNA
RNA
protein
Transcription
Initiation
Elongation
Termination
Processing
Capping
Splicing
Polyadenylation
Turnover
Translation
Protein processing
Many places for control

4. 1.1 Template
The template strand is the strand
from which the RNA is actually
transcribed. It is also termed as
antisense strand.
The coding strand is the strand
whose base sequence specifies the
amino acid sequence of the encoded
protein. Therefore, it is also called as
sense strand.

5. G C A G T A C A T G T C
5' 3'
3' C G T C A T G T A C A G 5' template
strand
coding
strand
transcription
RNA
G C A G U A C A U G U C
5' 3'

6. Transcription bubble

7. Initiation
 RNA polymerase
 core subunits (α α’ β β’ ω)
 Sigma factor (σ)
 Core + σ = holoenzyme
 Binds promoter sequence
 Catalyzes “open complex” and
transcription of DNA to RNA

8. TRANSCRIPTION PROCESS:
INITIATION  ELONGATION 
TERMINATION
“Closed
Complex”
“Open
complex”
(~14 bps)
(Transcription initiation is considered complete when the first two ribonucleotides of an RNA chain are
linked by a phosphodiester bond.)

9. (primary transcript)
TRANSCRIPTION PROCESS:
INITIATION  ELONGATION 
TERMINATION

10. The Holoenzyme:
Direction of transcription
Upstream Downstream
Prokaryotic RNA polymerase
-Core pol + 70 factor = RNA Pol Holoenzyme
-70 factor recognizes and binds to the promoter region

11. Bacterial sigma factors
 Sigma factors are “transcription factors”
 Different sigma factors bind RNAP and recognize
specific -10 ,-35 sequences
 Helps melt DNA to expose transcriptional start site
 -10 (binding and melting of DNA )
 : Pribnow box (prok.)
 : Hogness box (euk.)
 -35 (recognition seq. for binding of polymerase)

12. Promoter and terminator sequences of a gene tell the RNA
polymerase where to start and stop transcription

13. 5 channels of enzyme
 NTP uptake channel
 RNA exit channel
 Downstream DNA channel
 Non template strand (NT) channel
 Template strand (T) channel