Transcriptional repressor. Binds specifically to GATA sequences and represses expression of GATA-regulated genes at selected sites and stages in vertebrate development. Regulates chondrocyte proliferation and differentiation. Executes multiple functions in proliferating chondrocytes, expanding the region of distal chondrocytes, activating proliferation in columnar cells and supporting the differentiation of columnar into hypertrophic chondrocytes. Interacts with RNF4; regulates TRPS1 repressor activity. Interacts specifically with the activator form of GLI3 (GLI3A) but not with the repressor form (GLI3R). In the embryo, expression is detected in both visceral and skeletal tissues. Found in the maxilla, mandible, snout, prospective phalanges and in the femoral head within the developing hip. Also expressed in the hair follicles. Detected prior to 7.5 dpc, with peak levels at around 11.5 dpc. In the developing limbs and face, levels are highest at 13.5 dpc and decline dramatically thereafter. Sumoylated. Sumoylation in the repressor domain inhibits the transcription repression activity. Sumoylation on Lys-1201 is the major site. Appears to be sumoylated on multiple sites (By similarity).