MPF and cyclin: modelling of the cell cycle minimum oscillator

The cell cycle appears to be controlled by the interplay between two protein complexes, MPF and cyclin. Their interactions play an essential role in the structure of the oscillator governing the cell cycle. There seems to be no general agreement on this latter crucial question. Two different mechanisms are proposed: (i) cyclin and p34 kinase combine to form an oligomer with MPF activity; (ii) cyclin enzymatically activates the passage from inactive pre-MPF to active MPF, with the postulate that MPF initiates cyclin degradation. We have modelled these two hypotheses to see whether both actually lead to oscillatory behaviour. The p34-cyclin oligomerization does so without any difficulty. With the second mechanism, however, the strict hypothesis that cyclin degradation is activated by MPF must be re-examined: the system only oscillates if, in disappearing, the MPF and the cyclin react with each other stoichiometrically. The model also demonstrates that it is useless to seek cyclic control of cyclin proteolysis.