The Two Hats of SOS

Abstract
Son of sevenless (SOS) is a guanine nucleotide exchange factor that activates Ras in response to growth factor stimulation. SOS also appears to serve as a guanine nucleotide exchanger for Rac and, thus, may be involved in cytoskeleton reorganization. Nimnual and Bar-Sagi discuss how these two activities of SOS can be regulated and how SOS may be recruited to different cellular locations through interactions with the adaptor proteins Grb2 and E3b1.