Answer :
Final answer:
Drosha is the enzyme that catalyzes the initial processing of miRNAs in the nucleus.
Explanation:
The enzyme that catalyzes the initial processing of miRNAs in the nucleus is Drosha. MiRNAs are small (~23 nt) RNA molecules that control gene expression at the post-transcriptional level. They are synthesized from hairpin precursors and processed by two duplex-specific endonucleases, Drosha and Dicer. Drosha catalyzes the cleavage of the primary miRNA transcript, while Dicer is responsible for the production of mature miRNAs.
