FIGURE 8.

Regulation of Ikaros activity by phosphorylation at the novel sites. A, the balance between hyperphosphorylation of Ikaros (by CK2 kinase or other unidentified kinases) and its dephosphorylation by unknown phosphatases cause Ikaros to reversibly localize at PC-HC. B, a working model of the regulation of TdT expression during the early stages of thymocyte differentiation (modified from Trinh et al. (20)). Dephosphorylation of Ikaros during thymocyte differentiation (mimicked by induction of differentiation with PMA plus ionomycin) increases the DNA binding affinity of Ikaros toward the D′ regulatory region, resulting in the displacement of Elf-1 and the repression of the TdT gene.