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 ca- pable 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 ad- dition to ribosomal RNA, transfer RNA and, presumably, "messenger" RNA are required for protein synthesis in reticulocytes. It vitro stud- ies have shown that reticulocytes cannot syn- thesize 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.