Final answer:
RNA polymerase II of eukaryotes is primarily responsible for transcribing mRNA, which is processed after transcription to become mature mRNA ready for translation.
Step-by-step explanation:
RNA polymerase II of eukaryotes is responsible for transcribing mRNA. This enzyme is located in the nucleus and synthesizes all protein-coding nuclear pre-mRNAs. Eukaryotic pre-mRNAs undergo extensive processing after transcription to become mature mRNAs that are ready to be translated. It is important for transcribing the overwhelming majority of eukaryotic genes. While RNA polymerase II is associated with mRNA synthesis, RNA polymerase I is involved in transcribing rRNA, and RNA polymerase III is responsible for the transcription of tRNA and some rRNA.