Purification of a p47 phosphoprotein from Xenopus laevis oocytes and identification as an in vivo and in vitro p34cdc2 substrate

This paper describes the purification of a 47 kDa protein from Xenopus laevis oocytes that becomes phosphorylated when the oocytes undergo meiotic maturation. This protein (p47) is part of a high molecular mass complex containing at least two other proteins of molecular mass 30 and 36 kDa. This complex can be isolated from stage VI oocytes before maturation. We obtained a pattern for phosphopeptides in p47 phosphorylated in vivo very similar to that of the purified protein phosphorylated in vitro by p34cdc2 (a H1 kinase which is a component of the M-phase promoting factor) and [gamma-32P]ATP. Therefore, the purified p47, already described as a marker of MPF activity, is the first reported in vivo substrate for the cell division control kinase.