MEI4, a meiosis-specific yeast gene required for chromosome synapsis.

The MEI4 gene product is required for meiotic induction of recombination and viable spore production in the yeast Saccharomyces cerevisiae. DNA sequence analysis shows that the MEI4 gene encodes a 450-amino-acid protein bearing no homology to any previously identified protein. The MEI4 coding region is interrupted by a small intron located near the 5' end of the gene. Efficient splicing of the MEI4 transcript is not dependent on the MER1 protein, which is required for splicing the transcript of another meiotic gene, MER2. Expression of a mei4::lacZ fusion gene is meiosis-specific and depends on both heterozygosity at the mating-type locus and nutrient limitation. Northern (RNA) blot hybridization analysis suggests that MEI4 gene expression is regulated at the level of transcription. A functional MEI4 gene is not required for meiotic induction of transcription of the MER1, MER2, MEK1, RED1, SPO11, or RAD50 gene. Cytological analysis of mei4 mutant strains during meiotic prophase demonstrates that the chromosomes form long axial elements that fail to undergo synapsis. The meiosis II division is delayed in mei4 strains.