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First published online 4 December 2007
doi: 10.1242/jcs.019489

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Regulation of gene expression during M-G1-phase in fission yeast through Plo1p and forkhead transcription factors

¹ Division of Biochemistry and Molecular Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
² Institute of Cell and Molecular Biology, University of Edinburgh, Edinburgh, EH9 3JR, UK
³ Stem Cell Biology and Developmental Genetics, National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, UK

^* Author for correspondence (e-mail: C.McInerny{at}bio.gla.ac.uk)

Accepted 16 October 2007

In fission yeast the expression of several genes during M-G1 phase is controlled by binding of the PCB binding factor (PBF) transcription factor complex to Pombe cell cycle box (PCB) promoter motifs. Three components of PBF have been identified, including two forkhead-like proteins Sep1p and Fkh2p, and a MADS-box-like protein, Mbx1p. Here, we examine how PBF is controlled and reveal a role for the Polo kinase Plo1p. plo1⁺ shows genetic interactions with sep1⁺, fkh2⁺ and mbx1⁺, and overexpression of a kinase-domain mutant of plo1 abolishes M-G1-phase transcription. Plo1p binds to and directly phosphorylates Mbx1p, the first time a Polo kinase has been shown to phosphorylate a MADS box protein in any organism. Fkh2p and Sep1p interact in vivo and in vitro, and Fkh2p, Sep1p and Plo1p contact PCB promoters in vivo. However, strikingly, both Fkh2p and Plo1p bind to PCB promoters only when PCB-controlled genes are not expressed during S- and G2-phase, whereas by contrast Sep1p contacts PCBs coincident with M-G1-phase transcription. Thus, Plo1p, Fkh2p and Sep1p control M-G1-phase gene transcription through a combination of phosphorylation and cell-cycle-specific DNA binding to PCBs.

Key words: Cell cycle, Fission yeast, Mbx1p, Plo1p, Forkhead, Transcription