Experimental demonstration that the protein encoded by the Wilm's tumor (WT1) gene represses transcription. (a) Reporter gene construct (CAT gene is chloramphenicol acetyl transferase and transfers an acetyl group from acetyl coenzyme A, CoA, to chloramphenicol to produce acetyl chloramphenicol). (b) Structure of three different forms of WT1 generated by alternative splicing of WT1 mRNA. The carboxy terminal region of WT1 (orange) contains four C2H2 zinc fingers; WT1-KTS has an insertion of three amino acids in the DNA-binding region of WT1; WT1-17AA has a 17 amino acid sequence inserted into the WT1 sequence outside the DNA-binding region. (c) Autoradiogram of reaction products from CAT assay. The control had no WT1. These results show that WT1 must bind to the EGR-1 promoter region in order to exert its repression activity.