Growth- and nutrient-dependent G1/S transcription factor upregulation is controlled at the transcriptional level and is critical for proliferation in poor nutrient conditions

Ensuring size homeostasis in cell populations requires individual cells to pass a critical size threshold at the G1/S transition of the cell cycle where they commit to division. This threshold gates the onset of a massive transcription program that drives division. How is the G1/S program activated? Using sensitive quantitative imaging methods, we discovered that the key G1/S transcription complexes (SBF: Swi4-Swi6, MBF: Mbp1-Swi6, G1/S TFs) are limiting with respect to their DNA target sites in small daughter cells, and gradually accumulate in G1 phase to levels permitting saturation of target promoters.