Synthesis of Ribonucleic Acid in Rabbit Blood Cells in Vivo.

Erythroid cells constitute a model particularly suitable for study of the relationship between cell maturation and nucleic acid and protein synthesis. Circulating reticulocytes, nonnucleated cells capable of prolonged protein synthesis, are derived from cells in the bone marrow that proceed from an apparently multipotential nucleated stem cell through various stages of increasingly mature or differentiated cell types (2-5). Protein synthesis in reticulocytes proceeds on ribosomes (6, 7), in particular those ribosomes characterized by sedimentation coefficients in excess of 110 S, referred to as polyribosomes (8-10). In addition to ribosomal RNA, transfer RNA and, presumably, "messenger" RNA are required for protein synthesis in reticulocytes. It vitro studies have shown that reticulocytes cannot synthesize RNA (8). The present investigations were designed to determine when, in the course of in vivo maturation of erythroid cells, the RNA of reticulocytes is synthesized. In these experiments, the synthesis of RNA in rabbit erythroid cells in vivo was evaluated by following the time course of incorporation of administered PS2 into cellular RNA. The findings indicate that RNA of reticulocytes is synthesized in a relatively early precursor cell stage of erythroid cell maturation. RNA, once synthesized, can remain functional through the reticulocyte stage. Our study also provides evidence that nucleated leukocytes, in contrast to reticulocytes, can synthesize RNA.