Final answer:
The core structure of RNA polymerase in prokaryotes, such as E. coli, includes five polypeptide subunits: two identical α subunits, β, β', and σ. The first four comprise the core enzyme, while σ is specifically for transcription initiation. Together, they form the holoenzyme, ensuring accurate transcription.
Step-by-step explanation:
Five Common Subunits of RNA Polymerase II
The enzyme RNA polymerase in prokaryotes, such as E. coli, is made of five polypeptide subunits that play distinct roles in the transcription process. These subunits are often denoted by the Greek letters α, α, β, and β', with the two α subunits being identical. The α subunits are crucial for assembling the polymerase on the DNA, the β subunit binds to the ribonucleoside triphosphate which becomes part of the mRNA molecule, and the β' subunit binds the DNA template strand. The fifth subunit, denoted by the Greek letter σ, has a specific role in transcription initiation, ensuring that the polymerase begins to synthesize mRNA from the proper initiation site. Without σ, the core enzyme would start transcription at random sites, leading to nonsensical mRNA sequences. Collectively, these subunits assembled together form the holoenzyme.