Abstract
Purified, bacterially expressed PH domains of Sos1, IRS-1, betaARK, and PLCdelta1 were analyzed functionally by means of microinjection into full grown, stage VI Xenopus laevis oocytes. Whereas the PH domains from IRS-1, betaARK, or PLCdelta1 did not show any effect in the oocytes, injection of the purified Sos1 PH domain resulted in induction of significant rates of germinal vesicle breakdown and meiotic maturation. Furthermore, the Sos1 PH domain exhibited also significant synergy with insulin or coinjected normal Ras protein in induction of germinal vesicle breakdown, although it did not affect the rate of progesterone-induced maturation. These results suggest that purified, isolated PH domains retain, at least in part, their functional specificity and that Xenopus oocytes may constitute a useful biological system to analyze the functional role of the Sos1 PH domain in Ras signaling pathways.
Highlights
Pleckstrin homology (PH)1 domains are modular domains of about 100 amino acids present in a variety of signaling and cytoskeletal proteins, which were initially defined by their homology with the internal repeats of pleckstrin, a major protein kinase C substrate in platelets [1, 2]
Whereas the PH domains from IRS-1, ARK, or PLC␦1 did not show any effect, purified hSos1 PH domain was able to induce maturation when injected alone and exhibited significant synergy with insulin or coinjected normal Ras protein in induction of germinal vesicle breakdown (GVBD), it did not affect the rate of progesterone-induced maturation
We report in this paper that the isolated, purified PH domain of Sos1 exhibits functional biological activity in signal transduction processes involved in X. laevis oocyte maturation
Summary
Vol 271, No 30, Issue of July 26, pp. 18272–18276, 1996 Printed in U.S.A. Isolated Sos PH Domain Exhibits Germinal Vesicle Breakdown-inducing Activity in Xenopus Oocytes*. The Sos PH domain exhibited significant synergy with insulin or coinjected normal Ras protein in induction of germinal vesicle breakdown, it did not affect the rate of progesterone-induced maturation These results suggest that purified, isolated PH domains retain, at least in part, their functional specificity and that Xenopus oocytes may constitute a useful biological system to analyze the functional role of the Sos PH domain in Ras signaling pathways. Whereas the PH domains from IRS-1, ARK, or PLC␦1 did not show any effect, purified hSos PH domain was able to induce maturation when injected alone and exhibited significant synergy with insulin or coinjected normal Ras protein in induction of GVBD, it did not affect the rate of progesterone-induced maturation These results suggest that purified, isolated PH domains retain, at least in part, their functional specificity and that Xenopus oocytes offer a useful biological system to analyze their functional roles in signaling pathways
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