What is the primary enzyme that catalyzes transcription in bacteria?

• A. RNA polymerase holoenzyme
• B. DNA polymerase III
• C. DNA ligase
• D. Helicase

Answer: (A)

Transcription in bacteria is carried out by RNA polymerase, the enzyme that builds RNA from a DNA template. The form that can start transcription is the RNA polymerase holoenzyme, which is the core enzyme plus a sigma factor. The sigma factor recognizes promoter sequences and helps form the open complex, so transcription can begin. Once initiation happens, the sigma factor often dissociates and the core enzyme carries on elongation, making the RNA strand in the 5' to 3' direction without needing a DNA primer. The other enzymes listed—DNA polymerase III, DNA ligase, and helicase—are involved in DNA replication or repair rather than transcription: polymerase III copies DNA, ligase seals nicks, and helicase unwinds the double helix.