Binds to MCB elements (Mlu I cell cycle box) found in the promoter of most DNA synthesis genes. Transcriptional activation by MBF has an important role in the transition from G1 to S phase. It may have a dual role in that it behaves as an activator of transcription at the G1-S boundary and as a repressor during other stages of the cell cycle. Component of the transcription complex MCB-binding factor (MBF) composed of SWI6 and MBP1. Interacts with MSA1. Present with 521 molecules/cell in log phase SD medium.