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We find no difference in the rate of translation of OL-and /3-globin mRNA in cell-free extracts of rabbit reticulocytes (about 200 s per chain at 25") nor in the rate of release of completed globin chains from polyribosomes (about 15 s per chain).In these reactions, as well as incubation of intact reticulocytes, each /3-globin mRNA contains 30 to 40% more ribosomes than each oc-mRNA.These results imply that each /3-mRNA initiates synthesis of about 40% more p-globin than each ol-mRNA initiates synthesis of a! chains.Hence, reticulocytes must contain 30 to 40% more ar-mRNA than /3 in order to synthesize equal numbers of the two hemoglobin chains.This conclusion is consistent with results of a previous indirect measure of the relative amounts of CYand P-globin mRNA (Lodish, H. F.
Lodish et al. (Thu,) studied this question.