Chromatin conjugate protein A24 is cleaved and ubiquitin is lost during chicken erythropoiesis

The content of protein A24, an adduct of histone 2A and ubiquitin, was studied during chicken erythropoiesis. The amount of protein A24 was negligible in transcriptionally inactive mature chicken erythrocyte nuclei and 6-fold higher in the transcriptionally active nuclei of erythroid cells from phenylhydrazine-treated chickens. The decreased amount of protein A24 in the mature cells was offset by the relatively increased amount of histone 2A. A loss of free ubiquitin was also noted. In contrast, the amounts of high mobility group proteins 1,2, and E were essentially constant. Inasmuch as cleavage of the ubiquitin---histone 2A bond of protein A24 and loss of ubiquitin accompanied transcriptional shutdown during erythropoiesis, the presence of protein A24 and ubiquitin in premature polychromatic erythrocytes may reflect the presence of potentially active and transcribing chromatin structures.