Nucleolus

The nucleolus (/njuːˈkliːələs/ or /ˌnjuːkliˈoʊləs/, plural nucleoli /njuːˈkliːəˌlaɪ/ or /ˌnjuːkliˈoʊlaɪ/) 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.

History

Until 1964 little was known about the function of the nucleolus, even though it could be easily seen through microscopy and was recognized as part of the nucleus. During that year, a study of nucleoli by John Gurdon and Donald Brown in the African clawed frog Xenopus laevis generated increasing interest in the function and detailed structure of the nucleolus. They found that 25% of the frog eggs had no nucleolus and that such eggs were not capable of life. Half of the eggs had one nucleolus and 25% had two. They concluded that the nucleolus had a function necessary for life. In 1966 Max L. Birnstiel and Hugh Wallace showed via hybridization experiments that genes within nucleoli code for ribosomal RNA.