The t(11;22) chromosomal translocation specifically linked to Ewing sarcoma and primitive neuroectodermal tumor results in a chimeric molecule fusing the amino-terminus-encoding region of the EWS gene to the carboxyl-terminal DNA-binding domain encoded by the FLI-1 gene. As the function of the protein encoded by the EWS gene remains unknown, we investigated the putative role of EWS in RNA polymerase II (Pol II) transcription by comparing its activity with that of its structural homolog, hTAFII68. We demonstrate that a portion of EWS is able to associate with the basal transcription factor TFIID, which is composed of the TATA-binding protein (TBP) and TBP-associated factors (TAFIIs). In vitro binding studies revealed that both EWS and hTAFII68 interact with the same TFIID subunits, suggesting that the presence of EWS and that of hTAFII68 in the same TFIID complex may be mutually exclusive. Moreover, EWS is not exclusively associated with TFIID but, similarly to hTAFII68, is also associated with the Pol II complex. The subunits of Pol II that interact with EWS and hTAFII68 have been identified, confirming the association with the polymerase. In contrast to EWS, the tumorigenic EWS-FLI-1 fusion protein is not associated with either TFIID or Pol II in Ewing cell nuclear extracts. These observations suggest that EWS and EWS-FLI-1 may play different roles in Pol II transcription.