CD79B (also known as B29, Ig beta and B cell antigen receptor complex-associated protein beta-chain) is a 37-39 kDa member of the Ig-Superfamily. It is expressed on B cells, and forms a covalent heterodimer with CD79A. This complex interacts noncovalently with membrane Ig, forming the B cell antigen receptor. Within this complex, membrane Ig detects antigen while CD79A/B initiates signaling. CD79B is also required for formation of pre-B cells during B cell development. Mature mouse CD79B is a 203 amino acid (aa) type I transmembrane glycoprotein (aa 26-228). It contains an extracellular region with one V-type Ig-like domain (aa 41-132) and an ITAM-containing cytoplasmic domain (aa 181-228). CD79B may migrate as two bands in SDS-PAGE. One defines the standard 37 kDa form, while a second represents one of two possible isoforms, the first of which is an underglycosylated full-length CD79B, and the second of which is an alternative splice form that likely lacks the C-terminal 32 amino acids. Mouse CD79A and CD79B share only 24% aa identity. Over aa 29-158, mouse CD79B shares 54% and 78% aa identity with human and rat CD79B, respectively.