||The SH2 (Src Homology 2) domain is a structurally conserved motif that contains two alpha helices and seven beta strands and is found in a variety of proteins that are involved in signal transduction throughout the cell. Specifically, the SH2 domain targets SH2 domain-containing proteins to tyrosine-phosphorylated sites, an event that can trigger a protein-protein interaction cascade which may ultimately effect gene expression and cellular function. Shb (SH2 domain-containing adapter protein b， Shd (SH2 domain-containing adapter protein d， She (SH2 domain-containing adapter protein e) and Shf (SH2 domain-containing adapter protein f) are SH2 domain-containing proteins that play various roles throughout the cell. Shb is a widely expressed protein that localizes to both the cell membrane and the cytoplasm and plays an important role in signal transduction, mainly by linking activated proteins to downstream signaling targets, thereby propagating a signal cascade. Unlike Shb, Shd and Shf are thought to function as adaptor proteins, the former of which may be involved in apoptotic regulation.