Involved in B-cell receptor (BCR)-induced Ca(2+) mobilization from intracellular stores. Promotes Lyn-mediated phosphorylation of IP3 receptors 1 and 2 (By similarity). Interacts with LYN, ITPR1 and ITPR2. Specifically expressed in spleen. Highly expressed in immature B-cells and recirculating B-cells, and at low levels in pro-B and pre-B cells. Phosphorylated on tyrosines upon BCR activation. Truncated C-terminus.