Final answer:
RNA polymerase in prokaryotes needs all five subunits, including the sigma (σ) subunit for specific initiation, to create functional RNA. The core enzyme, lacking the σ subunit, cannot initiate transcription correctly and would lead to random and non-functional mRNA production.
Step-by-step explanation:
To create RNA, the RNA polymerase in prokaryotes such as E. coli requires all five subunits: alpha (α), alpha (α), beta (β), beta prime (β'), and omega (ω). These five subunits together form the holoenzyme. The core enzyme, which consists of two α subunits, β, and β', is capable of elongation but is not sufficient for the correct initiation of transcription.
The σ subunit is essential for transcription initiation as it confers specificity for the start sites, ensuring that transcription begins at the right location. Without the σ subunit, the core enzyme would bind to DNA at random sites, resulting in non-functional mRNA. The omega (ω) subunit has not been mentioned as essential but is typically included in the holoenzyme composition.