Nucleolus

The nucleolus (plural nucleoli) is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus of cells. Its function is to transcribe ribosomal RNA (rRNA) and assemble it within the cell.

The nucleolus ultrastructure can be visualized through an electron microscope, while the organization and dynamics can be studied through fluorescent protein tagging and fluorescent recovery after photobleaching (FRAP). Antibodies against the PAF49 protein can also be used as a marker for the nucleolus in immunofluorescence experiments. Malfunction of nucleoli can be the cause for several human diseases. It takes up to about 25% of the nuclear volume.