Translational control of hemoglobin synthesis by an initiation factor required for recycling of ribosomes and for their binding to messenger RNA.

The continued recycling of ribosomes during protein synthesis in rabbit reticulocyte lysates at 37 degrees requires an initiation factor whose activity is rapidly lost in the absence of added heme. Partially purified factor (i) fully maintains the polysomes; (ii) inhibits the association of 40S and 60S ribosomal subunits into single ribosomes; (iii) promotes the quantitative entry of added 60S subunits into polysomes; (iv) allows the accumulation of ribosomal subunits, instead of single ribosomes, when initiation is blocked with aurin tricarboxylate; and (v) is absolutely required for the binding of globin messenger RNA to ribosomes.These properties suggest that this mammalian initiation factor functions analogously to bacterial IF-3. In addition, the translational control of globin synthesis by heme is exerted, directly or indirectly, through this factor.