Required for proper signaling by sevenless. May act to stimulate the ability of Sos to catalyze Ras1 activation by linking sevenless and Sos in a signaling complex (By similarity). Interacts with autophosphorylated sev via SH2 domain and Sos and Dab via SH3 domains. Binds to tyrosine phosphorylated Dab via the SH2 domain (By similarity). Belongs to the GRB2/sem-5/DRK family.