Globin chain synthesis in single erythroid bursts from cord blood: studies on gamma leads to beta and G gamma leads to A gamma switches.

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Abstract
Erythroid bursts from cord or adult [human] blood were grown in methylcellulose cultures (3 IU of erythropoietin/plate). On day 13, single bursts were picked up and reincubated for 16-24 h with [3H]leucine. Radioactive globin chains [.alpha.,.beta.,G.gamma., and A.gamma. (Ala-136)] were analyzed by isoelectric focusing on polyacrylamide gels and fluorography or CM cellulose chromatography. .alpha. to non-.alpha. globin radioactivity ratios were close to 1. In single cord blood bursts, the values of .gamma.-to-.beta. and G.gamma.-to-A.gamma. ratios were spread over a large spectrum and further characterized by a continuous rather than a bimodal distribution. The G.gamma.-to-A.gamma. ratios demonstrated in single bursts appeared to be directly correlated with the respective .gamma.-to-.beta. ratios. The .gamma. .fwdarw. .beta. and the G.gamma. .fwdarw. A.gamma. switches were apparently mediated via mechanisms modulating the relative activities of the different genes in the non-.alpha. globin gene cluster rather than via selection of clones committed to preferential synthesis of .beta. and A.gamma. globins. In contrast with the results obtained with cord blood, individual adult blood bursts synthesize a lower and relatively more uniform amount of .gamma. globin chains.