Proliferation-sensitive nuclear phosphoprotein "dividin" is synthesized almost exclusively during S phase of the cell cycle in human AMA cells.

Studies of the polypeptides synthesized by normal and transformed human cultured cells under a variety of physiological conditions have revealed a basic 54-kDa protein NEPHGE 10a, whose rate of synthesis is sensitive to changes in the rate of cell proliferation. This nuclear phosphoprotein, which we have termed "dividin" (present only in populations of cells committed to divide), is synthesized almost exclusively during the S phase of the cell cycle of transformed human amnion cells (AMA). Dividin synthesis is first detected late in G1 near the G1/S transition border, reaches a maximum late in S phase, and declines thereafter. As expected for an S phase-specific protein, no detectable synthesis of dividin was observed in growth-arrested normal human cultured cells of epithelial and fibroblast origin. These findings suggest a role for this protein in events leading to DNA replication and cell division.