Reduction of perturbations in leucine incorporation in synchronous cultures of Schizosaccharomyces pombe

Good synchronous cultures of the fission yeast Schizosaccharomyces pombe can be made by selecting small cells from the Beckman JE-6 elutriator rotor. More important, the rate of leucine incorporation in controls shows far less perturbation than after selection from tube gradients. Elutriation may therefore be the best available method for reducing perturbations in selection synchronized cultures. Synchronous cultures of yeasts (and other cells) have been produced for more than a decade by selecting fractions from an exponential phase culture after centrifuging in a gradient in tubes or in zonal rotors (Mitchison & Carter, 1975). Although this method is satisfactory in the fission yeast Schizosaccharomyces pombe for measuring some cellular components, e.g. DNA, we have found recently that it causes serious perturbations in other components. These perturbations appear in synchronous cultures and also in control cultures (Mitchison & Carter, 1975) which are put through most of the synchronizing pro-cedure but which are not finally selected for size and are therefore asynchronous with respect to the cell cycle. Two examples are shown in Fig. 1 (a) and (b) for the rate of leucine incorporation, which ought to increase exponentially in an unperturbed culture. As ofte