Induced erythropoiesis in the mouse spleen was employed to study chromosomal protein synthesis during erythroid cell development. Splenic erythropoiesis occurring after phenylhydrazine induced hemolysis can be divided into an early phase during which nuclear RNA polymerase activity and RNA production are maximal and a late phase in which hemoglobin synthesis and DNA accumulation are maximal. Chromatin was isolated from splenic tissue during both the early and late phases of erythropoiesis as well as from non-anemic animals. The total protein content of chromatin from the early erythroid phase was greater than that of chromatin from the late erythroid phase or from non-anemic controls. The increase was due to a coordinate increase in the concentration of both histone and nonhistone proteins. During late erythropoiesis, the concentration of each returned to pre-anemic levels. Total histone synthesis increased 2.6-fold during early erythropoiesis as compared with the pre-anemic state and remained elevated in late erythropoiesis. The increase in histone synthesis was due to an increase in the synthesis of all five major histone proteins. Nonhistone protein synthesis was more active than that of histones in the pre-anemic spleen and rose only slightly during early erythropoiesis, returning to preanemic levels during late erythropoiesis. Fractionation of nonhistone proteins on SDS-urea polyacrylamide gels revealed complex patterns with significant differences between the pattern of erythroid spleen non-histone proteins and that of the pre-anemic spleen. Analysis of the incorporation of 3H-valine into the non-histone proteins indicated that during early erythropoiesis there was a generalized increase in nonhistone protein synthesis. During the late erythroid phase, the decline in non-histone protein synthesis was most marked for the higher molecular weight proteins.
ASJC Scopus subject areas
- Cell Biology