Cell size modulates SBF and Whi5 chromatin association to regulate the Start of the budding yeast cell cycle.

Cell size influences SBF and Whi5 chromatin association dynamics, regulating the Start transition in budding yeast with significant shifts observed at specific cell sizes.

• Why it matters: Understanding how cell size controls the timing of cell cycle entry is crucial for insights into growth regulation and cell cycle fidelity, especially since multiple mechanisms beyond Whi5 influence this process.
• What they did: Using single-molecule fluorescence microscopy, researchers quantified chromatin association of Whi5 and SBF in live Saccharomyces cerevisiae cells, revealing size-dependent changes in their mobility and abundance.
• The result: Findings show that larger cells have decreased Whi5 chromatin association and increased SBF association, with these shifts coinciding with the activation of SBF target genes, elucidating how size signals are transmitted to the genome to trigger division.