Fig. 9. Plo1p, Fkh2p and Sep1p regulation of genes expressed during the M-G1 phase in fission yeast. Expression of genes during late M phase in fission yeast is controlled by a transcription factor complex containing at least three proteins, the MADS box protein Mbx1p, and the forkhead transcription factors Fkh2p and Sep1p. Fkh2p and Sep1p both control cell cycle expression through cell-cycle-specific binding to PCB sequences, with Fkh2p repressing and Sep1p activating gene expression. Additionally, Mbx1p changes in a cell-cycle-specific manner. It is directly bound to and phosphorylated by Plo1p, whereby Plo1p stimulates transcription by binding to PCB DNA after Fkh2p. As plo1⁺ and fkh2⁺ are also transcribed at M-G1 phase, and both contain PCB sequences in their promoters to which Plo1p and Fkh2p bind, these genes regulate their own expression.