Tissue distribution of GAP1(IP4BP) and GAP1(m): two inositol 1,3,4,5-tetrakisphosphate-binding proteins.

Two members of the GAP1 family, GAP1(IP4BP) and GAP1(m), have been shown to bind the putative second messenger Ins(1,3,4,5)P4 with high affinity and specificity, though other aspects of their behaviour suggest that in vivo, whereas GAP1(IP4BP) may function as an Ins(1,3,4,5)P4 receptor, GAP1(m) may be a receptor for the lipid second messenger PtdIns(3,4,5)P3. As a step towards clarifying their cellular roles, we describe here how we have raised and characterised antisera that are specific for the two proteins, and used these to undertake a comprehensive study of their tissue distribution. Both proteins are widely expressed, but there are several clear differences between them in the tissues that show the highest levels of expression.