The
nucleolus ( or , plural
nucleoli or ) is the largest structure in the
nucleus of
eukaryotic cells, where it primarily serves as the site of ribosome synthesis and assembly. Nucleoli also have other important functions like assembly of
signal recognition particles and playing a role in the cell's response to stress. Nucleoli are made of proteins and
RNA and form around
specific chromosomal regions. Malfunction of nucleoli can be the cause of several human diseases.