On the mechanism of delayed inhibition of protein synthesis in heme-defecient rabbit reticulocyte lysates.

In the absence of added hemin, protein synthesis in a rabbit reticulocyte lysate declines abruptly (shuts off) after about 5 min at 30 degrees. In these studies we have examined the basis for the lag period preceding shut-off. The initiation factor that binds Met-tRNAf, previously shown to be rate-limiting in inhibited, heme-deficient lysates, is found to be used stoichiometrically in the presence of excess inhibitor. We suggest that a principal effect of the inhibitor is to impair the recycling of the Met-tRNAf-binding factor; the lag period is attributable largely to the presence of a pool of excess Met-tRNAf-binding factor, which, once used in initiation, cannot be recycled because of the action of the inhibitor.