What distinguishes eukaryotic RNA polymerase II from prokaryotic RNA polymerase?

• A. RNA Pol II is capable of initiating transcription without any other factors.
• B. RNA Pol II transcribes mRNA in eukaryotes and requires transcription factors; prokaryotic RNA polymerase does not.
• C. Prokaryotic RNA polymerase is a holoenzyme; eukaryotic Pol II is a single subunit.
• D. Pol II is a DNA helicase.

Answer: (B)

Transcription initiation in eukaryotes relies on a set of transcription factors that assemble with RNA polymerase II to form a preinitiation complex at promoter regions, and Pol II is the enzyme that produces mRNA in the cell. This need for multiple initiation factors is the biggest difference from prokaryotic transcription, where the core RNA polymerase can start transcription with a sigma factor guiding it to promoter sequences, without the same expanded set of separate initiation factors. So, RNA polymerase II transcribes mRNA and requires transcription factors, while prokaryotic RNA polymerase can initiate with its sigma factor and does not depend on those eukaryotic-style factors.