THIS ISSUE

摘要

The cell cycle couples growth and cell division to ensure the consistent size and shape of individual cells. This involves a vast array of genes and proteins, and requires sophisticated mechanisms to keep them acting in step. Two groups focus on different points in the cell cycle of the yeast Saccharomyces cerevisiae, and find that in each case, positive feedback keeps the process on the rails. Skotheim et al. studied the Start checkpoint in the G1 cell cycle phase, where cells irreversibly commit to cell division. Single-cell analysis reveals that Start is a positive feedback-dependent switch coordinating the simultaneous transcription of a large group of cell cycle genes with the budding of a daughter cell. Holt et al. studied the onset of anaphase in mitosis, at which chromosome pairs separate simultaneously. Cohesion between sister chromatids is dissolved by the enzyme separase, which is held in check by securin. A positive feedback loop regulating the ubiquitination and destruction of securin makes anaphase a switch-like event.