Process of Transcription in Bacteria

• The sigma (σ) factor associates with the core RNA polymerase to form the holoenzyme.
• The holoenzyme recognises and binds to the promoter region on the DNA.​

The promoter contains two key sequences upstream of the transcription start site:

• –10 region (Pribnow Box): Rich in A-T base pairs; easily melts open (consensus: TATAAT)
• –35 region: Important for initial recognition by σ factor

The DNA double helix unwinds and opens at the initiation site (+1), forming an open complex.​ Once transcription begins, the σ factor dissociates from the holoenzyme - it is only needed for initiation.

• RNA polymerase moves along the template strand in the 3'→5' direction.​
• New RNA is synthesised in the 5'→3' direction.​

The substrates used are ribonucleoside triphosphates (NTPs) — ATP, GTP, CTP, and UTP.​

• Note: Uracil (U) pairs with Adenine (A) in DNA → unlike DNA, where Thymine pairs with A

The two DNA strands re-anneal behind the polymerase as it moves forward. Only one strand (the template strand) is read at a time.

Transcription termination in bacteria occurs by two mechanisms:

• A single RNA polymerase synthesises all types of RNA (mRNA, tRNA, rRNA).
• Initiation starts when RNA polymerase binds to the promoter region.
• Elongation occurs via complementary base pairing of nucleotides.
• Termination happens at a terminator sequence, releasing RNA.
• No mRNA processing; transcription and translation occur simultaneously.