Isolation and Characterization of Modified Globin Messenger Ribonucleic Acid from Erythropoietic Mouse Spleen

Messenger RNA activity for α and β chains of hemoglobin has been detected in the RNA of free polyribosomes from splenic erythroblasts following phenylhydrazine injection of mice. This activity accumulates rapidly from 66 hours after injection, reaching a maximum at 114 hours. After polyacrylamide gel electrophoresis, the messenger RNA activity for both α and β chains is found in a single RNA band having an estimated molecular weight of 150,000. In contrast, globin messenger RNA isolated from rabbit reticulocytes has an estimated molecular weight of 190,000. When rabbit reticulocyte lysate was mixed with mouse spleens prior to homogenization, the RNA isolated was deficient in the 190,000-dalton reticulocyte mRNA, but contained an excess of the 150,000-dalton RNA which directed the synthesis in vitro of predominantly rabbit α and β chains. Thus, we infer that the globin mRNA obtained from mouse spleen erythroblasts has been modified by ribonuclease activity during its isolation. This modified mRNA is also deficient in polyadenylic acid, as judged by its behavior on oligo(dT) cellulose chromatography. We conclude that globin mRNA lacking a portion of its untranslated structure may still retain considerable mRNA template activity. Moreover, since globin messenger RNA activity is isolated at a specific time of cellular differentiation in the erythropoietic mouse spleen, this system appears well suited for the study of regulation of transcription.