A novel target for the Wilms' tumour suppressor protein (WT1) is bound by a unique combination of zinc fingers

All isoforms of the Wilms' tumour suppressor protein, WT1, contain four consecutive zinc fingers which facilitate DNA binding. The predominant WT1 transcript contains a 9 base pair insertion resulting in an additional three amino acids, lysine-threonine-serine (KTS), between zinc fingers 3 and 4. WT1 zinc fingers 2, 3 and 4 are highly homologous to the zinc fingers of the early growth response gene, EGR1. However, only WT1-KTS is capable of binding an EGR1 consensus site. In contrast, the previously described genomic fragment, +P5 (D1S3309E), is bound by both WT1-KTS and WT1+KTS. In this study, the region within +P5 to which both WT1-KTS and WT1+KTS bind was defined as 5-GGAGAGGGAGGATC-3'. EGR1 did not bind +P5. By creating zinc finger deletions, we demonstrate that zinc finger 1, but not zinc finger 4, is critical for +P5 binding; whereas zinc finger 4, but not 1, is necessary for the binding of WT1 target sites within EGR1, PDGF A chain and IGF2 promoters. Thus, zinc finger usage can vary with target and +P5 may represent a novel type of WT1 binding site, the physiological relevance of which must be investigated.