Discussion
Globin synthesis in the absence of heme in RBC is regulated by the phosphorylation of this factor :
Answer: B
The factor phosphorylated is eIF2.
In reticulocytes, globin synthesis is matched to heme supply. When heme is scarce, the heme-regulated inhibitor (HRI) kinase becomes active and phosphorylates the α subunit of eIF2. Phosphorylated eIF2 binds its recycling factor eIF2B too tightly, so eIF2-GDP is not exchanged to eIF2-GTP, initiator tRNA is not delivered, and translation initiation stops. Heme inhibits HRI, so adequate heme keeps globin synthesis running.
EF1 and EFG are elongation factors, and eIF3 binds the small subunit and helps recruit mRNA; none is the target of this control.
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