Changes in nuclear phosphoproteins have been followed during the course of development of the avian erythrocyte. Both young reticulocytes and mature erythrocytes are capable of incorporating 32P1 into nuclear proteins, the bulk of the activity occurring in the nonhistone protein fraction. Both phosphorylation and dephosphorylation of these proteins occur at faster rates in the younger cells. As maturation proceeds, nuclear levels of both phosphoprotein kinase and protein-bound phosphorus fall several-fold. Thus changes in the metabolism and composition of these nuclear phosphoproteins correlate with changes in the structure and activity of the nucleus.
Peer Reviewed
http://deepblue.lib.umich.edu/bitstream/2027.42/32855/1/0000231.pdf