Outline the steps of transcription initiation in bacteria.

• A. Sigma factor binds core RNA polymerase to form holoenzyme; holoenzyme binds promoter; DNA unwinding to form open complex; RNA synthesis begins; sigma factor released after promoter escape.
• B. RNA polymerase binds promoter; DNA unwinding; RNA synthesis; termination.
• C. Sigma factor binds promoter; open complex forms; RNA is translated.
• D. Initiation complex forms at terminator; RNAP moves along producing RNA.

Answer: (D)

Transcription initiation in bacteria starts when the sigma factor binds the core RNA polymerase to form the holoenzyme. This holoenzyme recognizes and binds promoter sequences, correctly positioning the enzyme at the start site. DNA unwinds at the promoter to create an open complex, exposing the template strand so RNA synthesis can begin. The RNA chain is initially short, and after a few nucleotides are added, the polymerase escapes the promoter and the sigma factor dissociates, allowing the enzyme to enter elongation. This sequence is distinct from other processes, and translation occurs later in the cell cycle, using the mRNA produced during transcription.