Prolonged mitosis versus tetraploid checkpoint - How p53 measures the duration of mitosis

Degradation of p53 requires transcription, and therefore inhibitors of transcription cause p53 accumulation. When transcription resumes, the p53 that accumulated in turn induces p21. During mitosis, chromosomes are condensed, the nuclear envelope is dissolved and transcription is absent. If a cell stays in mitosis too long, (e.g. mitotic arrest caused by Taxol or nocodazole), then p53 accumulates. This explains how p53 can measure mitotic time and perhaps represents the most fundamental function of p53.