MITOTIC APPARATUS OF A GIANT AMEBA . SOLUBILITY PROPERTIES AND INDUCTION OF ELONGATION

Mitotic apparatuses released from giant, multinucleate amebae directly into solutions of different pH, ionic strength, or composition exhibit precise solubility borderlines. The isolated MA is stable at pH 6.0 or below in most buffer solutions, at pH 5.0 or below in a chelating buffer solution, in KCl or CaCl2 solutions below 0.5 M at pH 6.0, between 10-3 M and 0.4 M CaCl2 at every pH tested, and at pH 6.8 or below in solutions containing 10-4 M CaCl2. Cells in mitosis could utilize changes near one of these solubility borderlines to control the mutual repulsion of MA-microtubule components and hence could control, in part, the relative rates of MA assembly and disassembly. The isolated MA appears structurally complete, but an in vitro reconstruction of normal MA function is not obtained with the isolated, stabilized unit. However, a brief MA elongation similar to anaphase movement can be induced during isolation into a solution containing magnesium and ATP. When the changes that occur in dividing cells are clarified, the effects of several of those changes may be understandable in terms of the MA properties described here. © 1969.