Abstract
The enzyme PI 3-kinase seems to mediate extraordinarily diverse cellular responses to growth factors. In his Update Perspective, Hemmings offers an explanation by outlining the evidence for a common target of the phospholipid signaling molecules generated by PI 3-kinase—the pleckstrin homology (PH) domains located on at least 100 cellular proteins, which could mediate the diverse responses of cells. On p. 1927 of this issue, Klarlund et al . report the isolation of one of these PH domain-containing proteins, GRP1.