Transcriptional activation by the Ewing's sarcoma (EWS) oncogene can be cis-repressed by the EWS RNA-binding domain

The Ewing's sarcoma (EWS) oncogene contains an N-terminal transcriptional a ctivation domain (EWS activation domain, EAD) and a C-terminal RNA-binding domain (RBD). Although it has been established that the EAD is a potent tra ns-activation domain that is required for the oncogenic activity of several EWS fusion proteins (EFPs), the precise function of the RBD and the normal role of intact EWS are poorly characterized, Here we show that a cis-linke d RBD can strongly and specifically repress trans-activation by the EAD, Fu sion proteins containing the RBD are expressed at normal levels, are nuclea r-localized, and can bind to DNA both in vitro and in vivo, demonstrating t hat the RBD represses transactivation directly at the promoter. The RNA rec ognition motif within the RBD is not required for repression, whereas regio ns of the RBD containing multiple RGG motifs play a critical role. The find ing that the RBD can antagonize transcriptional activation by EWS provides the first direct evidence of a role for the RBD in transcription. Further s tudies of the repression phenomenon should illuminate key molecular interac tions that distinguish EWS from EFPs and provide insights into the normal c ellular function of EW.