Importin-9 recognizes ETS transcription factor winged-helix fold, mediating nuclear import

Protein trafficking between the cytoplasm and the nucleus is a fundamental process in eukaryotic cell biology, essential for maintaining cellular homeostasis and regulating gene expression. While many nuclear proteins utilize well-characterized linear nuclear localization signals (NLSs) for their transport, a significant number of crucial nuclear proteins, including many transcription factors, lack such predictable motifs. This knowledge gap hinders a complete understanding of how these proteins reach their functional sites within the nucleus. ETS transcription factors, vital regulators of cellular processes like proliferation, differentiation, and apoptosis, are often dysregulated in diseases like cancer. Elucidating their precise nuclear import mechanisms is critical for fundamental biology and therapeutic strategies.

To uncover the mechanism of ETS transcription factor nuclear import, researchers employed a combination of structural and biochemical approaches. They utilized high-resolution crystallography to determine the atomic structure of the interaction between Importin-9 and the ETS domain. Complementary quantitative binding assays were performed to characterize the affinity and specificity of this interaction, mapping the key recognition elements involved. The study aimed to identify and functionally characterize the specific NLS within ETS proteins and its cognate nuclear import receptor, providing molecular details of this essential cellular process.