Autoregulated expression of Schizosaccharomyces pombe meiosis-specific transcription factor Mei4 and a genome-wide search for its target genes.

The Schizosaccharomyces pombe mei4(+) gene encoding a forkhead transcription factor is necessary for the progression of meiosis and sporulation. We searched for novel meiotic genes, the expression of which is dependent on Mei4p, since only the spo6(+) gene has been assigned to its targets. Six known genes responsible for meiotic recombination were examined by Northern blotting, but none were Mei4 dependent for transcription. We determined the important cis-acting element, designated FLEX, to which Mei4p can bind. The S. pombe genome sequence database (The Sanger Centre, UK) was scanned for the central core heptamer and its flanking 3' sequence of FLEX composed of 17 nucleotides, and 10 candidate targets of Mei4 were selected. These contained a FLEX-like sequence in the 5' upstream nontranslatable region within 1 kb of the initiation codon. Northern blotting confirmed that 9 of them, named mde1(+) to mde9(+), were transcriptionally induced during meiosis and were dependent on mei4(+). Most mde genes have not been genetically defined yet, except for mde9(+), which is identical to spn5(+), which encodes one of the septin family of proteins. mde3(+) and a related gene pit1(+) encode proteins related to Saccharomyces cerevisiae Ime2. The double disruptant frequently produced asci having an abnormal number and size of spores, although it completed meiosis. We also found that the forkhead DNA-binding domain of Mei4p binds to the FLEX-like element in the putative promoter region of mei4 and that the maximum induction level of mei4 mRNA required functional mei4 activity. Furthermore, expression of a reporter gene driven by the authentic mei4 promoter was induced in vegetative cells by ectopic overproduction of Mei4p. These results suggest that mei4 transcription is positively autoregulated.