 Multisite phosphorylation of Sic1 is thought to time Sic1 ubiquitination and destruction, and by extension, the timing of S-phase entry.In the G1 phase of the cell cycle, Sic1 binds tightly to the Cdc28-Clb complex and inhibits it.Low Cdc28-Clb activity leads to the disassembly of the mitotic spindle, the assembly of the prereplicative complex and initiation of bud formation in yeast.