1. Transcription of rRNA Genes: Ribosomal DNA is transcribed by RNA polymerase I to produce a primary rRNA transcript. In humans, this precursor is known as 45S pre-rRNA.
2. Processing of Pre-rRNA: The 45S pre-rRNA undergoes extensive processing, including cleavage and chemical modifications, to generate mature rRNA species (18S, 5.8S, and 28S rRNA in eukaryotes).
3. Assembly of Ribosomal Subunits: rRNAs combine with ribosomal proteins, imported from the cytoplasm, to form the small (40S) and large (60S) ribosomal subunits.
4. Transport to the Cytoplasm: Once assembled, the ribosomal subunits are transported out of the nucleus through nuclear pores to the cytoplasm, where they participate in translation.
