SF-1 interacts with the NF-YA subunit, but not the NF-YB or NF-YC subunits. A physical interaction between NF-Y and SF-1 was examined by a GST interaction assay. A, GST-SF-1 or GST alone was bound to glutathione sepharose beads and incubated with in vitro translated 35S-labeled NF-Y subunits, as indicated. GFP serves as a negative control and Ptx1 protein serves as a positive control for interaction with SF-1. B, GST alone, GST-NF-YA, or GST-NF-YB was incubated with 35S-labeled SF-1 or GFP, as indicated. GST alone serves as a control for the specificity of the interaction. Input shows 10% of the amount of in vitro translated protein used for the interaction.