show Abstracthide AbstractThe core promoter of protein-encoding genes plays a central role in regulating transcription. M1BP is a transcriptional activator that associates with a core promoter element known as Motif 1 that resides at thousand of genes in Drosophila. To gain insight into how M1BP functions, we identified an interacting protein called GFZF. GFZF had been previously identified in genetic screens for factors involved in maintenance of hybrid inviability, the G2-M DNA damage checkpoint, and RAS/MAPK signaling but its contribution to these processes was unknown. Previous evidence indicated that GFZF resides in the cytoplasm. Here, we show that GFZF resides in the nucleus and functions as a transcriptional co-activator. In addition, we show that GFZF is a glutathione S-transferase(GST). Thus, GFZF is the first transcriptional co-activator with intrinsic GST activity, and its identification as a transcriptional co-activator provides an explanation for its role in numerous biological processes. Overall design: 2 M1BP, 3 GFZF, 3 controls (this includes 2 Preimmune, 1 NoIgG)