Regulation of the Wilms' tumour suppressor protein transcriptional activation domain

The Wilms' tumour suppressor protein WT1 contains a transcriptional regulat ory domain that can either activate or repress transcription depending upon its cellular environment. The mechanistic basis for this dichotomy is uncl ear however. Here, we dissect the transcriptional regulatory domains of WT1 . We find that a region within the domain of WT1 attributed to transcriptio nal repression is a potent suppressor of the activation domain at several p romoters and in different cell types. In vitro transcription analysis sugge sts that the mechanism of suppression of the activation domain occurs at th e level of transcription initiation. Furthermore we find that the WT1 suppr ession domain is able to inhibit a heterologous activation domain when fuse d in cis. Dissection of this domain resulted in the delineation of a 30 ami no acid region that was sufficient to confer suppression of a transcription al activation domain both in vivo and in vitro. Additionally, we find that the WT1 transcriptional activation domain interacts with the general transc ription factor TFIIB and that this interaction is not affected by the suppr ession domain. Taken together, these studies suggest that the suppression d omain of WT1 interacts with a cosuppressor protein to mediate inhibition of the WT1 transcriptional activation domain.