The nucleolus also participates in the formation of signal recognition particles and plays a role in the cell's response to stress.

[7] Theodor Schwann in his 1939 treatise described that Schleiden had identified small corpuscles in nuclei, and named the structures "Kernkörperchen".

[8][9] In addition to these peculiarities of the cytoblast, already made known by Brown and Meyen, Schleiden has discovered in its interior a small corpuscle (see plate I, fig.

Sometimes only the external sharply-defined circle of this ring can be distinguished, with a dark point in the centre,—occasionally, and indeed most frequently, only a sharply circumscribed spot.

As it will frequently be necessary to speak of this body in the following treatise, I will for brevity’s sake name it the “nucleolus,” (Kernkorperchen, ‘nucleus-corpuscle.”)Little was known about the function of the nucleolus until 1964, when a study[10] of nucleoli by John Gurdon and Donald Brown in the African clawed frog Xenopus laevis generated increased interest in its function and detailed structure.

In 1966, Max L. Birnstiel and collaborators showed via nucleic acid hybridization experiments that DNA within nucleoli codes for ribosomal RNA.

Reflecting the substantial increase in the DNA intergenic region, an original fibrillar component would have separated into the FC and the DFC.

In eukaryotes, the RNA-modifying enzymes are brought to their respective recognition sites by interaction with guide RNAs, which bind these specific sequences.

In higher eukaryotes and plants, the situation is more complex, for the 5S DNA sequence lies outside the NOR and is transcribed by RNA Pol III in the nucleoplasm, after which it finds its way into the nucleolus to participate in the ribosome assembly.

The genes encoding these r-proteins are transcribed by Pol II in the nucleoplasm by a "conventional" pathway of protein synthesis (transcription, pre-mRNA processing, nuclear export of mature mRNA, and translation on cytoplasmic ribosomes).

[22] In addition to its role in ribosomal biogenesis, the nucleolus is known to capture and immobilize proteins, a process known as nucleolar detention.