Previous studies have suggested that the differentiated state of meiosis in yeast is regulated primarily at the transcriptional level. This study reports a case of posttranscriptional regulation of a gene whose product is essential for meiosis. The MER2 gene is transcribed in mitosis as well as meiosis; however, the transcript is spliced efficiently to generate a functional gene product only in meiosis. Meiotic levels of splicing depend on the MER1 gene product, which is also essential for meiosis and which is produced only in meiotic cells. Therefore, at least one of the functions of the MER1 protein is to mediate splicing of the MER2 transcript. Genetic data suggest that the MER1 gene may also be responsible for splicing the transcript of at least one other gene.