Transcription in prokaryotes involves the synthesis of RNA from a DNA template, occurring through initiation, elongation, and termination. Key components include bacterial RNA polymerase and the processes of rho-independent and rho-dependent termination. The document also highlights proofreading mechanisms and the simultaneous occurrence of transcription and translation in bacteria.

1. Transcription in
prokaryotes
G.KRANTHI KUMAR
3
rd
Pharm D

2. INTRODUCTION
 Synthesis of RNA by copying DNA template is known
as transcription.
 Only selected portion of the genome (exons)is
transcribed .
 RNA polymerase requires no primers it is a DNA
dependent RNA polymerase

3. Central dogma of biology
REPLICATION
DNA DNA
TRANSCRIPTION POST
TRANSCRIPTIONAL
MODIFICATION
RNA

6. The process of transcription takes place in three major
steps. They are :
1. Initiation.
2.Elongation.
3.Termination.

7. N
 Transcription is initiated by RNA Polymerase
holoenzyme from a specific region called promotor
sequence in DNA .
 Principle enzyme – Bacterial RNA Polymerase
 RNA Polymerase alone is called core Polymerase .
 Core polymerase consists of α,β,β’and ω sub units.

8.  Closed complex formation :
Binding of RNA polymerase holoenzyme
to promotor sequence.
 Open complex formation :
1. RNA polymerase holoenzyme separates
10-14 DNA basepairs extending from
-11 to +3 and this is called melting.
2. It leads to the formation of open
complex.
3. closed complex to open complex
isomerization

9. Teritiary complex formation :
1. If the enzyme synthesizes RNA <10
basepairs ,it does not elongate it
abortive initiation.
2. Because σ factor acts as a mimic of RNA
and blocks the RNA exit channel in open
complex.
3. When RNA polymerase synthesizes RNA >
10 base pairs , it ejects σ factor and RNA
elongates further and moves out through exit
channel. This is known as the teritiary complex

12. ELONGATION
 After the formation of teritiary complex the RNA
elongates further by the addition of dNTPs .
 The synthesized is proof read by hydrolytic editing.
Gre factor enhances the proof reading activity.
Pyrophospholytic editing is another proof reading
mechanism.

14. TERMINATION
 The process of termination can happen in two
different mechanisms. They are :
1. Rho – independent termination.
2. Rho – dependent termination.

15. termination
In this mechanism, transcription is terminated by
termination sequence in DNA.
Terminator sequence contains invert repeat causing
complementary pairing as transcript RNA form
hairpin structure.
Invert repeat is followed by a large number of T (~8
basepairs), in RNA “U” appears.
The load of hairpin structure isn’t tolerated by A=U
bps so RNA gets separated from RNA –DNA
heteroduplex.

16. Rho – dependent
termination
In this mechanism,transcription is terminated by rho
protein (ρ).
Rho protein is a single strand ATPase protein.
Rho protein binds to the single stranded RNA after
termination.
In bacteria, transcription and translation occurs
simultaneously so Rho protein binds to the mRNA
after translation i.e.,when translation is completed but
transcription is “ON”.