A beta-geo gene trap vector inserted into intron 1. Western blot analysis confirmed the absence of protein expression in extracts from primary fibroblasts. In primary fibroblasts levels of phophatidylinositol 3,5-biphosphate and phophatidylinositol 5-phosphate are significantly reduced while levels of phophatidylinositol 3-phosphate are elevated. (J:127106)