Biochemical characterization of human Ecdysoneless reveals a role in transcriptional regulation.

Ecdysoneless (Ecd) is an evolutionarily conserved protein and its function is essential for embryonic development in Drosophila and cell growth in yeast. However, its function has remained unknown until recently. Studies in yeast suggested a potential role of Ecd in transcription; however, Ecd lacks a DNA-binding domain. Using a GAL4-luciferase reporter assay and a GAL4 DNA-binding domain fusion with Ecd or its mutants, we present evidence that human Ecd has a transactivation activity in its C-terminal region. Importantly, further analyses using point mutants showed that a single amino acid change at either Asp-484 or Leu-489 essentially completely abolishes the transactivation activity of Ecd. We further demonstrate that Ecd interacts with p300, a histone acetyltransferase, and coexpression of Ecd with p300 enhances the Ecd-mediated transactivation activity. Ecd localizes to both nucleus and cytoplasm and shuttles between the nucleus and cytoplasm; however, it exhibits strong nuclear export. Based on previous yeast studies and evidence provided here, we suggest that Ecd functions as a transcriptional regulator. Our results indicate an important function of human Ecd and provide a basis to explore the transcriptional partners of Ecd.