KINETICS OF MPF AND HISTONE-H1 KINASE-ACTIVITY DIFFER DURING THE G2-PHASE TO M-PHASE TRANSITION IN MOUSE OOCYTES

Maturation promoting factor (MPF) is universally recognized as the bio logical entity responsible for driving the cell cycle from G(2)- to M- phase. Histone H1 kinase activity is widely accepted as a biochemical indicator of p34(cdc2) protein kinase complex activity and therefore M PF activity. In this paper we present results which indicate that duri ng the G(2)- to M-phase transition in mouse oocytes the dynamic of p34 (cdc2) related histone H1 kinase activity differs markedly from the bi ological activity of MPF as measured by classical cell fusion procedur es. MPF is activated just before germinal vesicle breakdown (GVBD) whe reas histone H1 kinase is activated 5-7 h later coincident with the fo rmation of the definitive first metaphase plate. The biological activi ty of MPF is merely reduced to about 50% of control levels by a short period of protein synthesis inhibition (1-2 h) and completely suppress ed after a prolonged period of inhibition (4-5 h). By contrast, inhibi tion of protein synthesis in mouse oocytes results in a rapid and comp lete suppression of histone H1 kinase activity. Therefore, biological MPF and histone H1 kinase activity should not be used in an interchang eable manner during the G(2)- to M-phase transition in mouse oocytes.