The Bcr gene was orginally identified by its presence in the chimeric Bcr-Abl oncogene. The amino-terminal region of Bcr contains an oligomerization domain, a serine/threonine kinase domain, and a region that binds SH2 domains. The middle of the protein has a PH domain and a region of sequence similarity to the guanine nucleotide exchange factors for the Rho family of GTP binding proteins. The carboxy-terminal region may be involved in a GTPase activating function for the small GTP-binding protein Rac. The function of wild type Bcr in cells remains unclear. PDGF receptor may use Bcr as a downstream signaling mediator. Research studies have shown that the Bcr-Abl fusion results in production of a constitutively active tyrosine kinase, which causes chronic myelogenous leukemia (CML). Tyr177 of Bcr is phosphorylated in the Bcr-Abl fusion protein, which plays an important role in transforming the activity of Bcr-Abl. Phosphorylated Tyr177 provides a docking site for Gab2 and GRB2.