Final answer:
Prokaryotes possess only one RNA polymerase, which transcribes all types of RNA, unlike eukaryotes that have three. This single RNA polymerase in prokaryotes consists of five subunits, with the sigma subunit being vital for transcription initiation.
Step-by-step explanation:
Prokaryotes have only one RNA polymerase that transcribes all types of RNA. This contrasts with eukaryotes, which have three distinct RNA polymerases (I, II, III) each responsible for synthesizing different types of RNA. In prokaryotes like E. coli, the RNA polymerase is composed of five polypeptide subunits: two α subunits, one β, one β', and a σ (sigma) subunit. The σ subunit is crucial for transcription initiation, directing the polymerase to the correct initiation sites and preventing random transcription that would result in nonfunctional protein production.
Prokaryotic RNA Polymerase Composition:
- α subunit: Necessary for assembling the polymerase on the DNA.
- β subunit: Binds the ribonucleoside triphosphate to form the mRNA molecule.
- β' subunit: Binds the DNA template strand.
- σ subunit: Contributes to transcriptional specificity and initiation.
The presence of only one RNA polymerase in prokaryotes is a simpler system compared to the multiple RNA polymerases in eukaryotes. Roger Kornberg was awarded the Nobel Prize for his research on RNA polymerase II in eukaryotes, which underscores the complexity of eukaryotic transcription.