Control of protein synthesis in reticulocyte lysates by haemin.

Abstract

PROTEIN synthesis in intact reticulocytes is severely restricted when iron is lacking in the incubation medium and can be restored by the addition of haemin1,2. In the lysate derived from such cells, protein is synthesized at a rate similar to that in intact cells3, but finishes abruptly after a few minutes unless haemin is added4,5. Haemin seems to act by stabilizing the capacity of the lysate to initiate protein synthesis, because in the absence of added haemin, polysomes disappear and their associated nascent chains are released4. It is not clear which step in initiation fails under these conditions. There is good evidence that native subunits and methionyl t-RNAF are directly involved in the process of initiation6–9. We examined the formation of complexes between the native subunits present in the lysate and met-tRNAF when lysates were synthesizing protein in the presence and absence of added haemin.