EWS/FLI alters 5'-splice site selection.

The chimeric gene EWS/FLI is present in at least 85% of Ewing's sarcomas as a result of chromosomal translocations. The resulting fusion protein contains the N terminus of the RNA-binding protein EWS and the ETS DNA-binding domain of the transcription factor FLI-1. Although EWS/FLI binds DNA and activates transcription, both EWS and EWS/FLI also interact with SF1 and U1C, essential components of the splicing machinery. Therefore, we tested the ability of EWS and EWS/FLI to alter 5'-splice site selection using an E1A gene in vivo splicing assay. We found that EWS/FLI, but not EWS, interfered with heterogeneous nuclear ribonucleoprotein A1-dependent splice site selection of E1A. Mutational analysis of EWS/FLI revealed that the ability to affect pre-mRNA splicing coincided with transforming activity. Therefore, EWS/FLI has the ability to influence splicing as well as transcription.