Purified maturation-promoting factor contains the product of a Xenopus homolog of the fission yeast cell cycle control gene cdc2⁺

In the fission yeast S. pombe, the M_r = 34 kd product of the cdc2⁺ gene (p34^cdc2) is a protein kinase that controls entry into mitosis. In Xenopus oocytes and other cells, maturation-promoting factor (MPF) appears in late G2 phase and is able to cause entry into mitosis. Purified MPF consists of two major proteins of M_r ≈ 32 kd and 45 kd and expresses protein kinase activity. We report here that antibodies to S. pombe p34^cdc2 are able to immunoblot and immunoprecipitate the ≈32 kd component of MPF from Xenopus eggs. The M_r ≈ 32 kd and 45 kd proteins exist as a complex that expresses protein kinase activity. These findings indicate that a Xenopus p34^cdc2 homolog is present in purified MPF and suggest that p34^cdc2 is a component of the control mechanism initiating mitosis generally in eukaryotic cells.