Abstract
The inhibition of protein synthesis in reticulocytes and their lysates caused by heme-deprivation is reversible on restoration of an optimal heme concentration. Inhibition is accompanied by the disaggregation of polyribosomes and the accumulation of components of the translational mechanism. By determining the fate of labeled globin 9S mRNA added to an unfractionated reticulocyte lysate cell-free system, we find that normal cellular mRNA accumulates during inhibition in 20S and 48S complexes and in a complex which sediments just ahead of the 80S ribosome dimer OD 260 peak (designated as ≥80S complex) 1 1 The “S-values” given in this paper are approximate values based on the sedimentation of the designated complex in the isokinetic sucrose gradients used in this study. The markers used for calibration were 9S globin mRNA, the 40S and 60S ribosomal subunits and the 80S initiation complex. . The 20S and ≥ 80S complexes are the major pools of stored mRNA which is readily translated if optimal heme conditions are restored. In the 48S complex, however, the mRNA remains non-functional, and the complex is abortive, probably as a result of deacylation of the Met. tRNA f.
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