Cotranslational heme binding to nascent globin chains

Globin synthesis in cell‐free extracts of rabbit reticulocytes was carried out in the presence of 3 H‐labeled hemin. Sucrose gradient centrifugation analysis revealed [ 3 H]hemin in the polyribosome fraction. The addition of puromycin resulted in the release of both [ 3 H]hemin‐ and [ 14 C]leucine‐labeled polypeptide from the polyribosomes. The data suggest cotranslational folding of the globin molecule on the ribosome and cotranslational heme binding to the nascent globin chain.