Purification of maturation-promoting factor, an intracellular regulator of early mitotic events.

TLDR

Maturation‑promoting factor induces germinal vesicle breakdown in Xenopus oocytes and can trigger metaphase in a cell‑free system. The authors aim to use highly purified preparations to uncover the mechanism of action of maturation‑promoting factor and to clarify the role of protein kinases in metaphase induction. A cell‑free assay monitored maturation‑promoting factor during its purification from unfertilized Xenopus eggs. Purification by ammonium sulfate precipitation and six chromatographic steps yielded a >3000‑fold enriched preparation that induces germinal vesicle breakdown within 2 hr in cycloheximide‑treated oocytes, with the most active fractions containing 45‑kDa and 32‑kDa proteins and a kinase that phosphorylates the endogenous 45‑kDa protein, histone H1, phosphatase inhibitor 1, and casein.

Abstract

Maturation-promoting factor causes germinal vesicle breakdown when injected into Xenopus oocytes and can induce metaphase in a cell-free system. The cell-free assay was used to monitor maturation-promoting factor during its purification from unfertilized Xenopus eggs. Ammonium sulfate precipitation and six chromatographic procedures resulted in a preparation purified greater than 3000-fold that could induce germinal vesicle breakdown within 2 hr when injected into cycloheximide-treated oocytes. Proteins of 45 kDa and 32 kDa were correlated with fractions of highest activity in both assays. These fractions contained a protein kinase activity able to phosphorylate the endogenous 45-kDa protein, as well as histone H1, phosphatase inhibitor 1, and casein. The highly purified preparations described here should help to identify the mechanism of action of maturation-promoting factor and to elucidate the role of protein kinases in the induction of metaphase.