CONTROL OF NUCLEAR DIVISION IN PHYSARUM-POLYCEPHALUM - COMPARISON OF CYCLOHEXIMIDE PULSE TREATMENT, UV IRRADIATION, AND HEAT SHOCK

The mechanism controlling the timing of synchronous nuclear division in the myxomycete Physarum polycephalum is studied by perturbing the normal cycle with inhibitors of protein synthesis, UV irradiation and exposure to elevated temperature. From changes in the timing of subsequent mitoses and in the protein: DNA ratio we propose that nuclear division is triggered by accumulation of an unstable activator, which is itself a protein or is dependent on synthesis of an unstable protein. The intermitotic period cannot be shortened below a minimum cycle time (Tmin) and we suggest that Tmin = TS + TA, where TS is the duration of S phase and TA is the time necessary to synthesize a full complement of activator. © 1979.