Answer:
sigma subunit
Step-by-step explanation:
Sigma subunit of RNA polymerase holoenzyme directs the enzyme towards the consensus sequences present upstream of the transcription start site. Completion of the initiation phase of transcription is followed by dissociation of sigma subunit from the transcription complex.
The protein NusA replaces the sigma subunit. The RNA polymerase leaves the promoter and starts the elongation
.