The Short-Lived RNA in the Cell Nucleus and its Possible Role in Evolution

This chapter discusses the possible role that a short-lived RNA in the cell nucleus plays in evolution. When cells were exposed to a radioactive RNA precursor, the RNA in the cell nucleus became labeled more rapidly than the RNA in the cytoplasm. When cells labeled in this way were transferred to a nonradioactive medium, it was observed that radioactivity disappeared from the nuclear RNA and appeared in the cytoplasmic RNA. The present study aims to show that the short-lived nuclear RNA molecules were transferred to the cytoplasm of the cell before being broken down; however, evidence indicates that these molecules were broken down within the nucleus. A small proportion of the RNA made in the nucleus at any one time could be an immediate macromolecular precursor of the stable RNA in the cytoplasm. Short-lived RNA molecules fail to assume the conformation that is necessary for functioning as templates, and in animal and higher plant cells, these molecules are eliminated within the nucleus.