Final answer:
The regulation of the human globin gene cluster involves translational control by hemin affecting the initiation factor eIF2B, and post-translational control where the phosphorylation state of eIF2B adjusts globin synthesis to match heme levels.
Step-by-step explanation:
The human globin gene cluster is regulated at various stages to ensure that globin proteins are synthesized in coordination with heme to form fully functional hemoglobin molecules in red blood cells. Two key stages in this regulation are translational and post-translational control. During the translational stage, hemin, a precursor to heme, regulates the initiation of translation of globin mRNAs by interacting with the eIF2B initiation factor which facilitates the GTP/GDP swap necessary for ongoing protein synthesis. In turn, this ensures that globin production does not exceed heme availability.
In the post-translational stage, the balance is further maintained by the phosphorylation status of eIF2B. When hemin is not in excess, it dissociates from HCR kinase, leading to the phosphorylation and inactivation of eIF2B, thus reducing globin synthesis to match heme levels. This intricate balance ensures that red blood cells produce the correct amount of globin relative to heme, crucial for the proper function of hemoglobin.