Daughter-specific transcription factors regulate cell size control in budding yeast

At the Start transition in G1, budding yeast cells integrate internal and external cues into an all-or-none commitment to a new round of cell division [1],[2]. Cell division is asymmetric, producing a smaller daughter cell and a larger mother cell [3]. Mother cells progress through Start more quickly than daughter cells [3],[4]. The regulation of G1 phase is composed of two independent modules separated by the nuclear exit of the transcriptional repressor whi5 [5]: a cell size sensing module, which extends g1 in small cells to allow additional growth before start [5], and a subsequent sizeindependent module [5],[6]. the fast and coherent transition between the two modules likely coincides with commitment to the cell cycle and is driven by transcriptional positive feedback [7]. the g1 cyclin cln3 is the most upstream activator of the start transition [8],[9],[10],[11],[12] and the main regulator of the size-sensing module. cln3 initiates inactivation of whi5 [13],[14] and expression of sbf/mbf dependent genes, including the g1 cyclins cln1 and cln2 [9],[11],[12],[15],[16]. subsequent positive feedback of cln1 and cln2 on sbf/mbf dependent transcription ensures fast and coherent commitment to the cell cycle [7].