||WT-1, the product of Wilms' Tumor suppressor gene Wt1, is a nuclear protein with structural motifs characteristic of transcription factors, including four C-terminal zinc fingers. While different pre-mRNA processing could result in 16 isoforms of the protein, the inclusion or exclusion of exon 5 and three amino acids (KTS) between zinc fingers 3 and 4 largely affects the activity of the WT-1 protein. Such a complex posttranscriptional regulation, particularly in splicing, may represent a major regulatory mechanism for tumorigenesis of the Wilms' tumor. With the inclusion of exon 5, WT-1 (+KTS) binds to both DNA and RNA and is RNase but not DNase sensitive. This form also colocalizes with splicing factor in a speckled nuclear particle, suggesting that WT-1 protein may function as both a transcription factor and a splicing regulator. The WT-1 protein (residue 1-449, including exon 5 and KTS) is expressed in baculovirus system and purified by an affinity column in combination with FPLC chromatography.