Activator of G1-specific transcription factors, MBF and SBF. Promotes both the timing of G1-specific gene transcription and cell cycle initiation. Associates with SBF- and MBF-regulated target promoters and this binding is maximal during the G1 phase, prior to maximum budding. Affects cell cycle initiation by advancing the timing of transcription of G1-specific genes. Overexpression advances the timing of SBF-dependent transcription and budding. Depletion delays both indicators of cell cycle initiation. Interacts with transcription complexes SCB-binding factor (SBF) and MCB-binding factor (MBF) at their target promoters. Interacts with MBP1 and SWI6. Expressed periodically during the cell cycle with peak mRNA levels occurring at the late M/early G1 phase, prior to budding, and levels decrease rapidly as cells enter into the S phase. In early G1 peak occurs (at protein level). Phosphorylated by CDC28.