In papillary renal cell carcinomas the TFE3 transcription factor becomes fused to the PSF and NonO pre-mRNA splicing factors and most commonly to a protein of unknown function designated PRCC. In this study we have examined the ability of the resulting PRCC ± TFE3 and NonO ± TFE3 fusions to activate transcription from the plasminogen activator inhibitor-1 (PAI-1) promoter. The results show that only fusion to PRCC enhanced transcriptional activation, indicating that the ability to enhance the level of transcription from endogenous TFE3 promoters is not a consistent feature of TFE3 fusions. In investigations of the normal function of PRCC we observed that PRCC expressed as a green¯uorescent fusion protein colocalizes within the nucleus with Sm premRNA splicing factors. It was also found that endogenous PRCC is coimmunoprecipitated by antibodies that recognize a variety of pre-mRNA splicing factors including SC35, PRL1 and CDC5. Association with the cellular splicing machinery is therefore, a common feature of the proteins that become fused to TFE3 in papillary renal cell carcinomas. Oncogene (2001) 20, 178 ± 187.

MGA2 and SPT23 are functionally and genetically redundant homologs in Saccharomyces cerevisiae. Both genes are implicated in the transcription of a subset of genes, including Ty retrotransposons and Tyinduced mutations. Neither gene is essential for growth, but mga2 spt23 double mutants are inviable. We have isolated a gene-specific activator, SWI5, and the Δ9 fatty acid desaturase of yeast, OLE1, as multicopy suppressors of an mga2Δ spt23 temperature-sensitive mutation (spt23-ts). The level of unsaturated fatty acids decreases 35–40% when the mga2Δ spt23-ts mutant is incubated at 37°. Electron microscopy of these cells reveals a separation of inner and outer nuclear membranes that is sometimes accompanied by vesicle-like projections in the intermembrane space. The products of Ole1p catalysis, oleic acid and palmitoleic acid, suppress mga2Δ spt23-ts and mga2Δ spt23Δ lethality and restore normal nuclear membrane morphology. Furthermore, the level of the OLE1 transcript decreases more than 15-fold in the absence of wild-type Mga2p and Spt23p. Our results suggest that Mga2p/Spt23p control cell viability by stimulating OLE1 transcription.