Erythroid bursts from cord or adult blood were grown in methylcellulose cultures (3 international units of erythropoietin per plate). On day 13, single bursts were picked up and reincubated for 16-24 hr with [ 3H]leucine. Radioactive globin chains [α,β,(G)γ, and (A)γ (Ala-136)] were analyzed by either isoelectric focusing on polyacrylamide gels and fluorography or carboxymethylcellulose chromatography. In all cases, α to non-α globin radioactivity ratios were close to 1. In single cord blood bursts, the values of both γ-to-β and (G)γ-to-(A)γ ratios were spread over a large spectrum and further characterized by a continuous rather than a bimodal distribution. Moreover, the (G)γ-to-(A)γ ratios demonstrated in single bursts appeared to be directly correlated with the respective γ-to-β ratios. These data suggest that both the γ→β and the (G)γ→(A)γ switches are mediated via mechanisms modulating the relative activities of the different genes in the non-α globin gene cluster rather than via selection of clones committed to the preferential synthesis of β and (A)γ globins. In contrast with the results obtained with cord blood, individual adult blood bursts synthesize a lower and hence relatively more uniform amount of γ globin chains.
|Number of pages||4|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - 1980|
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