Final answer:
In prokaryotes, the sigma subunit must dissociate from the RNA polymerase to facilitate elongation during the transcription process. The sigma subunit is only involved in the initiation stage of transcription, ensuring specificity in the mRNA synthesis.
Step-by-step explanation:
In prokaryotes, sigma subunit must dissociate to allow for elongation of the transcriptional complex. During the initiation phase of transcription, the sigma subunit (σ) of the prokaryotic RNA polymerase recognizes specific promoter sequences upstream of the transcription start site. Once transcription has been initiated, the σ subunit dissociates from the RNA polymerase, which then allows the core enzyme to proceed along the DNA template during the elongation phase. This dissociation is critical because it enables the RNA polymerase to synthesize mRNA in the 5' to 3' direction without the σ subunit, which only has a role in transcription initiation.
The holoenzyme, which is the complete complex of RNA polymerase with subunits α, α, β, β', and σ, is responsible for transcription initiation. Without the σ subunit, the core enzyme would lack specificity in starting mRNA synthesis, resulting in non-functional mRNA molecules.