Which of the following are NOT transcribed by RNA polymerase II ?
1. miRNA and some snRNA
2. mRNA and snoRNA
3. miRNA and snoRNA
4. tRNA and 5S rRNA

Understanding RNA Polymerases and Their Functions

In eukaryotic cells, three major RNA polymerases are responsible for transcribing different types of RNA:

• RNA Polymerase I: Transcribes most rRNA genes (except 5S rRNA)

• RNA Polymerase II: Transcribes mRNA, miRNA, snRNA, and some snoRNA

• RNA Polymerase III: Transcribes tRNA, 5S rRNA, and some snRNA and snoRNA

Why tRNA and 5S rRNA Are NOT Transcribed by RNA Polymerase II

The transcription of tRNA and 5S rRNA is carried out by RNA polymerase III, not RNA polymerase II, because:

• These RNA types have distinct promoter regions recognized specifically by polymerase III.

• RNA polymerase III operates in regions where structural RNAs like tRNAs and 5S rRNAs are needed in high amounts for protein synthesis.

What RNA Polymerase II Does Transcribe

RNA polymerase II is mainly responsible for the transcription of:

• mRNA – Messenger RNA, which encodes proteins

• miRNA – MicroRNA, which regulates gene expression post-transcriptionally

• snRNA – Small nuclear RNA, involved in RNA splicing

• Some snoRNA – Small nucleolar RNAs, involved in rRNA modification

Summary Table of RNA Polymerase Activity

Conclusion

The correct answer is tRNA and 5S rRNA, as these are not transcribed by RNA polymerase II, but rather by RNA polymerase III. Understanding the specific roles of each RNA polymerase helps clarify the complex regulation of gene expression in eukaryotic cells.