Which factor is important for termination of transcription?

The correct option is ρ(rho).

Transcription is the biological process where a DNA sequence is copied into a complementary RNA sequence by the enzyme RNA polymerase. This process consists of three main stages: initiation, elongation, and termination.

To understand the role of the different factors mentioned, we can look at their functions in transcription:
1. σ (sigma) factor: This is a protein needed for the initiation of transcription in bacteria. It enables specific binding of RNA polymerase to gene promoters.
2. ρ (rho) factor: This is an essential prokaryotic protein involved in the termination of transcription. It acts as an ATP-dependent helicase that binds to the growing RNA transcript, travels along it behind the RNA polymerase, and facilitates the release of the RNA transcript and the dissociation of the transcription complex at specific rho-dependent termination sites.
3. α (alpha) and γ (gamma) subunits: These are structural components or subunits of RNA polymerase and other cellular complexes, rather than transcription termination factors.

Therefore, the ρ (rho) factor is the key protein factor responsible for the termination of transcription in rho-dependent termination pathways.