COTRANSLATIONAL HEME-BINDING TO NASCENT GLOBIN CHAINS

Globin synthesis in cell-free extracts of rabbit reticulocytes was car ried out in the presence of H-3-labeled hemin. Sucrose gradient centri fugation analysis revealed [H-3]hemin in the polyribosome fraction. Th e addition of puromycin resulted in the release of both [H-3]hemin- an d [C-14]leucine-labeled polypeptide from the polyribosomes. The data s uggest cotranslational folding of the globin molecule on the ribosome and cotranslational heme binding to the nascent globin chain.