The regulation of ribosomal RNA synthesis and ribosomal assembly in the vertebrate lens

Experiments have been carried out to study the properties of ribosomal RNA synthesis and ribosomal assembly in cells having stable messenger RNA templates (adult epithelial cells in stationary phase and fiber cells) and rapidly turning-over templates (dividing epithelial cells). The data show that 45S and 30S precusor ribosomal RNA is synthesized in epithelial cells in a stationary phase and in fiber cells. These precursor ribosomal RNA's, however, are not chased into 28S and 18S RNA. Similar pulse-chase experiments with dividing epithelial cells of calf and adult lenses show a significant chase into 28S and 18S RNA. The data indicate that there is a regulation of ribosomal assembly at the step responsible for 28S and 18S RNA formation. The details of this regulation are discussed.