title: Phosphorylation changes associated with the early cell cycle in Xenopus eggs.
abstract: Enucleated and nondividing amphibian eggs undergo cyclic changes in cell morphology and in the level of maturation promoting factor (MPF) with a period similar to the early cleavage cycle. We show here that there is a corresponding phosphorylation and dephosphorylation of specific proteins associated with this fundamental cell cycle. M-phase is associated with a general increase in phosphatase activity and specific phosphorylation of a small set of M-phase proteins, reflected in an increased stochiometry of phosphate and increased turnover. At the end of metaphase and correlated with a drop in MPF the phosphoproteins are rapidly lost. By microinjecting M-phase phosphoproteins into arrested interphase and metaphase eggs we could show that the specific M-phase phosphorylation was not due to specificity in phosphatase action. The ability to segregate synthesis from phosphorylation demonstrates that regulation is not on the level of synthesis of the M-phase proteins. Taken together these data suggest that regulation of kinase activity in M-phase in the face of general rapid phosphate turnover in the egg plays an important role in the regulation of the fundamental mitotic cycle.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002453:Cell Cycle; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D007399:Interphase; D008540:Meiosis; D008677:Metaphase; D008938:Mitosis; D010063:Ovum / Q000166:cytology / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D014982:Xenopus laevis
chemical_list: D010710:Phosphates; D010750:Phosphoproteins; D000255:Adenosine Triphosphate