In Eukaryotes
Ribosomal protein synthesis in eukaryotes is a major metabolic activity that involves hundreds of individual reactions. It occurs, like most protein synthesis, in the cytoplasm just outside the nucleus. Individual large and small units are synthesized and imported into the nucleus through nuclear pores. These pores have a diameter of 120 nm and import 560,000 ribosomal proteins per minute into the nucleus with active transport. See nuclear import for more about the movement of the ribosomal proteins into the nucleus.
The rRNA is transcribed at the nucleolus, at a high speed, which contains all 45S rRNA genes. The only exception is the 5S rRNA which is transcribed outside the nucleolus. After transcription, the rRNA is put together with the ribosomal subunits to make a functioning ribosome. See nuclear export for more about the movement of the ribosomal subunit out of the nucleus.
Read more about this topic: Ribosome Biogenesis