Which class of RNA polymerase is responsible for transcribing most eukaryotic genes?

• A. RNA polymerase I
• B. RNA polymerase III
• C. RNA polymerase II
• D. RNA polymerase IV

Answer: (C)

RNA polymerase II is the enzyme that handles the bulk of gene transcription in eukaryotic cells. It transcribes protein-coding genes into messenger RNA and also many noncoding RNAs, such as certain small nuclear RNAs, which together make up the majority of transcripts in the cell. This enzyme works with a set of transcription factors to recognize promoters and initiate transcription, after which its largest subunit has a C-terminal domain that coordinates RNA processing steps like 5' capping, splicing, and 3' polyadenylation, producing mature mRNA ready for translation.

In contrast, RNA polymerase I is focused on ribosomal RNA genes, tRNA and 5S rRNA genes fall to RNA polymerase III, and RNA polymerase IV is a plant-specific enzyme involved in RNA-directed DNA methylation rather than general transcription. Because it transcribes the most genes, especially the mRNA-coding ones, RNA polymerase II is responsible for transcribing the majority of eukaryotic genes.