Gatekeeper of meiotic initiation in both male and female germ cells. In complex with STRA8, directly activates the transcription of a subset of critical meiotic genes playing a central role in cell-cycle switching from mitosis to meiosis. Temporal expression of MEIOSIN is required for meiotic entry decision. Interacts with STRA8. Contains a degenerate basic motif not likely to bind DNA.