The zinc finger domain confers transactivating activity in erythroid cells.

(A) NIH3T3, K562, and U937 cells were transiently transfected with a reporter plasmid containing 4 Gfi-1–specific binding sequences (4xGfi-1-SBS) in front of a basal thymidine kinase promoter (TK) along with either wild-type Gfi-1B or a series ofGfi-1B mutants. (B) K562 cells were transiently transfected with either wild-type or mutant SOCS-1 promoter along with wild-type Gfi-1B (left panel). NIH3T3 and K562 cells were transiently transfected with the wild-type SOCS-1 promoter along with either wild-typeGfi-1B or a series of Gfi-1B mutants (right panel). Luciferase activities were determined 24 hours after transfection and normalized to the Renilla luciferase activities of the internal control plasmid pRL-CMV. The fold increase in promoter activity was measured relative to that obtained with empty vector. The results are shown as the mean ± SD of triplicate transfections. G indicates Gfi-1B binding site; S, STAT binding site.