Final answer:
The core enzyme of prokaryotic RNA polymerase cannot initiate transcription correctly without the σ subunit; it requires the entire holoenzyme, including the σ subunit, for specific and functional transcription.
Step-by-step explanation:
The core enzyme of prokaryotic RNA polymerase, consisting of the subunits α, α, β, and β', is responsible for the elongation phase of transcription but lacks the specificity for transcription initiation. The σ subunit is critical during the initiation phase as it confers transcriptional specificity, ensuring that the polymerase starts synthesizing mRNA from the correct initiation site. Without the σ subunit, the core enzyme would transcribe mRNA from random sites, resulting in nonfunctional protein gibberish. The complete enzyme, including all five subunits (α, α, β, β', and σ), is known as the holoenzyme, which is capable of properly initiating and performing transcription.