BCR is one of the two genes in the BCR-ABL fusion protein, which is associated with the Philadelphia chromosome.

Although the BCR-ABL fusion protein has been much studied, the function of the normal BCR gene product is still not clear.

The protein has serine/threonine kinase activity and is a guanine nucleotide exchange factor for the Rho family of GTPases including RhoA.

The translocation produces a fusion protein that is encoded by sequence from both BCR and ABL, the gene at the chromosome 9 breakpoint.

Together these form an N-shaped structure, with the loop allowing the two helices to assume a parallel orientation.