Which factor is important for termination of transcription?

The correct answer is **ρ (rho)**.

In bacterial transcription, termination of RNA synthesis can occur by two main mechanisms: intrinsic (factor‑independent) termination and factor‑dependent termination. The factor‑dependent pathway requires a specific protein called the **rho factor**.

Here is how the rho factor functions step‑by‑step:

1. **Recognition of the Rut site** – After the RNA polymerase has transcribed a stretch of RNA that is rich in cytosine residues and poor in guanine, a sequence known as the **Rho Utilization (Rut) site** is exposed on the nascent RNA.

2. **Binding of rho** – The rho protein, which is a hexameric RNA‑dependent ATPase, binds to this Rut site. The binding is ATP‑dependent and positions rho on the RNA downstream of the polymerase.

3. **Translocation** – Using energy from ATP hydrolysis, rho translocates along the RNA in the 5'→3' direction toward the RNA polymerase.

4. **Catch‑up and destabilization** – When rho catches up to the paused RNA polymerase, it induces a conformational change that disrupts the transcription complex, causing the RNA‑DNA hybrid to unwind.

5. **Release of the transcript** – The destabilized complex releases the newly synthesized RNA, terminating transcription.

Thus, the presence and activity of the rho factor are essential for the **factor‑dependent termination** of transcription in prokaryotes. The other listed symbols (σ, γ, α) refer to different components (e.g., σ is the initiation factor that recognizes promoters) and are not directly involved in termination.