The Schaechter-Bentzon-Maaloe experiment and the analysis of cell cycle events in eukaryotic cells

The Schaechter-Bentzon-Maaloe (SBM) experiment, performed more than 40 years ago, provides an important lesson for the analysis of the eukaryotic cell cycle. Before this experiment, temperature shifts had been used to synchronize bacteria and determine the pattern of DNA synthesis during the bacterial division cycle. These experiments indicated that DNA replication occurred during a fraction of the division cycle with gaps before and after DNA synthesis, a pattern similar to the eukaryotic division cycle. The SBM experiment studied DNA replication during the division cycle by labeling an unperturbed culture with a short pulse of tritiated thymidine. All cells were found to be labeled, indicating that unperturbed cells synthesize DNA throughout the division cycle. Thus, the SBM experiment was a control experiment demonstrating that artifacts can be introduced by synchronization methods. The idea of an control experiment under unperturbed conditions is proposed for the analysis of data on cell-cycle-specific gene expression in yeast and mammalian cells.