Which factor is important for termination of transcription?

In the process of transcription, the synthesis of an RNA strand by RNA polymerase must eventually stop so that the newly made RNA can be released. This stopping step is called **termination of transcription**.

The factor that is specifically responsible for terminating transcription in many organisms, especially in bacteria, is the **ρ (rho) factor**.

Here is a step‑by‑step explanation of how the ρ factor works:

1. **Binding to the nascent RNA**
The ρ protein is a helicase that recognizes a particular, often rich in cytosine‑guanine (C‑G) sequence on the emerging RNA called the **ρ‑binding site**. It binds to this site once it becomes exposed as the RNA grows.

2. **ATP‑dependent translocation**
After binding, ρ uses the energy from ATP hydrolysis to move (or “track”) along the RNA in the 5′→3′ direction, chasing the RNA polymerase that is still attached to the DNA template.

3. **Catch‑up and RNA–DNA unwinding**
When ρ catches up to the RNA polymerase, its helicase activity unwinds the RNA–DNA hybrid within the transcription bubble. This destabilizes the interaction between the enzyme, the DNA template, and the RNA transcript.

4. **Release of the RNA transcript**
The unwinding causes the RNA strand to be released from the transcription complex, and the RNA polymerase dissociates from the DNA. At this point transcription is terminated.

Because the ρ factor performs these essential actions—binding, translocating, and unwinding—it is the key protein factor that **directly causes termination** of transcription in the ρ‑dependent termination pathway.

Other factors listed in the options, such as α, γ, or σ, have different roles (e.g., σ is involved in transcription initiation, α is a subunit of RNA polymerase, and γ can refer to various regulatory proteins), but they are **not** the primary agents that bring about termination.

Therefore, the correct answer is **ρ (rho) factor**, which is indispensable for the termination step of transcription.