Bacterial Transcription

Opposite strand is called the_______________-strand

\-the base sequence is identical to transcript

non-template or coding strand or sense

Transcription occurs in three stages

• Initiation • Elongation • Termination

Structural genes

– • Transcribed in to ……

• Constitutes about 90% of all genes

mRNA

Non Structural genes are not translated include

Ribosomes

Spliceosomes

Signal Recognition Particle

Telomerase

tRNA

\-35 sequence

T T G A C A

\-10 sequence (tata box)

TATAAT

the strength of a promoter is determined by …………….

how close the promoter sequence is to the consensus sequence

Initiation of transcription needs _____ __enzyme__

__for elongation__ ______ is enough

HOLO

CORE

core enzyme composition

alpha 2, B, B' ,omega

holo enzyme composition

alpha 2 B, B' ,omega, + SIGMA

B,B' :

catalytic subunit

Alpha 2:

keeps the complex together

Sigma:

recognizes promoter sequence (-10 & -35)

---Important to recognize -10 so you can open up helix at -10

Initiation of Transcription in Bacteria

1. **The RNA polymerase holoenzyme binds loosely to the DNA**
2. **It then scans along the DNA, until it encounters a promoter region**
3. **When it does, the sigma factor recognizes both the –35 and –10 regions**


1. **A region within the sigma factor that contains a helix-turn-helix structure is involved in a tighter binding to the DNA**
2. alpha helices bind to major groove
4. The binding of the RNA polymerase to the promoter forms the **closed complex**
5. Then, the open complex is formed when the TATAAT box in the -10 region is unwound
6. A short RNA strand is made within the open complex


1. sigma factor released

elongation phase

The core enzyme now slides down the DNA to synthesize an RNA strand


1. The open complex formed by the action of RNA polymerase is about 17 bases long
2. Behind the open complex, the DNA rewinds back into a double helix

On average, the rate of RNA synthesis is about___________ per second!

43 nucleotides

Termination of Bacterial transcription

• It occurs when the short RNA-DNA hybrid of the open complex is forced to separate

• This releases the newly made RNA as well as the RNA polymerase

E. coli has two different mechanisms for termination

1\. rho-dependent termination

• Requires a protein known as ρ (rho)

2\. rho-independent termination

• Does not require ρ

rho dependent termination

*rho-utilization site = (rut)*


1. rho protein binds to the rut site in RNA and moves towards the 3’ end
2. RNA pol transcribes a region that forms a stem loop & then proceeds to terminator
3. stem loop causes RNA pol to pause
4. during pause, rho protein catches up to open complex & separates RNA/DNA hybrid

ρ-independent termination is facilitated by two sequences in the RNA

1\. A uracil-rich sequence located at the 3’ end of the RNA

2\. A stem-loop structure upstream of the uracil-rich sequence

ρ-independent termination

1. U-rich RNA in RNA/DNA hybrid
2. stem loop causes RNA pol to pause
3. when paused, weekly bound U rich sequence is not able to hold RNA/DNA hybrid so termination occurs