Some thoughts on the origin of RNA, and the roles of ribosomes, the nucleolus and the nucleus.

The deciphering of DNA's structure led to the formulation of Crick's central dogma, implicit in which is that all RNA is chromosomal in origin. The detection of RNA synthesis at nucleolar sites, plus the similarity between r RNA and nucleolar RNA has firmly established the idea that the nucleolus is responsible for r RNA production. But neither of these considerations actually prove that this is so. An analysis of RNA synthesis in E coli suggests that its r RNA is not chromosomal in origin, but arises by semi conservative replication. The likelihood therefore exists that eukaryotic r RNA also arises by self replication and is not a product of the nucleolus. This concept is favoured by the behaviour of the nucleolus in the differentiating cell in which it seems to have an important role.