Yeast Two-Hybrid (Y2H) and GST Pull-down are two classic upstream technologies in protein-protein interaction research. The former leverages the separation property of the BD/AD domains of yeast transcription factors to achieve high-throughput screening of unknown interacting proteins via reporter gene activation, making it suitable for identifying novel pathway components. The latter fuses the bait protein with a GST tag to directly capture and verify the physical interactions between known proteins in vitro, often providing in vitro validation evidence for preliminary screening results. These two technologies are frequently used in combination, forming a complete upstream technical workflow for protein-protein interaction studies.