Unexpectedly large size of globin messenger ribonucleic acid

The globin messenger RNA of rabbit reticulocytes is identified on the basis of its presence in polysomes, absence from single ribosomes, and sedimentation coefficient of 9 S. Analysis of this RNA by electrophoresis in polyacrylamide gels provides evidence that its size is unexpectedly large (approximately 650 nucleotides) for a messenger coding for the 141 and 146 amino acids of a globin polypeptide. Reticulocyte RNA molecules were labeled in vivo with [(32)P]orthophosphate. Globin messenger RNA and transfer RNA appear to be synthesized late in erythropoiesis, whereas ribosomal RNA and 5S RNA are synthesized at the beginning stages of cytodifferentiation. At least one fragment of ribosomal RNA accumulates in erythrocytes in the terminal stages of maturation.