In BCR signaling, appears to function as a docking protein acting downstream of TEC and participates in a positive feedback loop by increasing the activity of TEC. Interacts with KIT and CSF1R (By similarity). Interacts with URI1; the interaction is phosphorylation-dependent and occurs in a growth-dependent manner. Phosphorylated on tyrosine by TEC. Phosphorylated on tyrosine by KIT (By similarity).