Transcription factor that plays an important role in the regulation of lymphocyte differentiation. Binds to GGGAA. Plays an essential role in regulation of B-cell differentiation, proliferation and maturation to an effector state. Involved in regulating BCL2 expression and controlling apoptosis in T-cells in an IL2-dependent manner. Homodimer. Heterodimer with other IKAROS family members. Interacts with IKZF4 AND IKZF5. Interacts with HRAS. Interacts with FOXP3; this interaction may be required for silencing target genes and regulating the suppressive activity of FOXP3-positive regulatory T-cells (Treg). Interacts with BCL21L isoform Bcl-X(L); this interaction blocks the anti-apoptotic role of BCL21L. Associates with histone deacetylase complexes containing HDAC1, MTA2 and SIN3A (By similarity). Interacts with IKZF1. Expression is restricted to lymphoid tissues. Expressed at highest levels in spleen and at lower levels in the thymus and bone marrow. First detected in more committed lymphoid progenitors and strongly up-regulated as these differentiate into pre-T and pre-B cell precursors. C2H2-type 5 and C2H2-type 6 mediate homodimerization and heterodimerization. Belongs to the Ikaros C2H2-type zinc-finger protein family.