The forkhead protein Fkh2 is a component of the yeast cell cycle transcription factor SFF

In the yeast Saccharomyces cerevisiae, the MADS-box protein Mcm1, which is highly related to mammalian SRF (serum response factor), forms a ternary co mplex with SFF (Swi five factor) to regulate the cell cycle expression of g enes such as SW15, CLB2 and ACE2, Here we show that the forkhead protein Fk h2 is a component of SFF and is essential for ternary complex formation on the SWI5 and ACE2 promoters. Fkh2 is essential for the correct cell cycle p eriodicity of SWI5 and CLB2 gene expression and is phosphorylated with a ti ming that is consistent with a role in this expression. Furthermore, invest igation of the relationship between Fkh2 and a related forkhead protein Fkh 1 demonstrates that these proteins act in overlapping pathways to regulate cell morphology and cell separation. This is the first example of a eukaryo tic transcription factor complex containing both a MADS-box and a forkhead protein, and it has important implications for the regulation of mammalian gene expression.