THE C-TERMINAL ZINC-FINGER OF GATA-1 OR GATA-2 IS SUFFICIENT TO INDUCE MEGAKARYOCYTIC DIFFERENTIATION OF AN EARLY MYELOID CELL-LINE

The GATA-1 and GATA-2 transcription factors, which each contain two ho mologous zinc fingers, are important hematopoietic regulators expresse d within the erythroid, mast cell, and megakaryocytic lineages. Enforc ed expression of either factor in the primitive myeloid line 416B indu ces megakaryocytic differentiation. The features of their structure re quired for this activity have been explored. The ability of 12 GATA-1 mutants to promote 416B maturation was compared,vith their DNA-binding activity and transactivation potential. Differentiation did not requi re any of the seven serine residues that are phosphorylated in vivo, a n N-terminal region bearing the major transactivation domain, or a C-t erminal segment beyond the fingers. Removal of a consensus nuclear loc alization signal following the second finger did not block differentia tion or nuclear translocation; The N-terminal finger was also dispensa ble, although its removal attenuated differentiation. In contrast, the C-terminal finger was essential, underscoring its distinct function. Remarkably, only 69 residues spanning the C-terminal finger were requi red to induce limited megakaryocytic differentiation. Analysis of thre e GATA-2 mutants led to the same conclusion. Endogenous GATA-1 mRNA wa s induced by most mutants and may contribute to differentiation. Becau se the GATA-1 C-terminal finger could bind its target site but not tra nsactivate a minimal reporter, it may direct megakaryocytic maturation by derepressing specific genes and/or by interacting with another pro tein which provides the transactivation function.