Transcription of mutS- and mutL-homologous genes during meiosis in Saccharomyces cerevisiae and identification of a regulatory cis-element for meiotic induction of MSH2.

We have analysed the levels of mRNA transcripts of the mutS- and mutL-homologous genes of the yeast Saccharomyces cerevisiae during the course of meiosis, by quantitative RT-PCR. We found that all mutS homologues (MSH1-6) were induced during meiosis, whereas no evidence for regulation of the mutL homologues (PMS1, MLH1-3) was obtained. Temporal expression patterns indicative of co-regulation were observed for the gene pairs MSH4/MSH5 and MSH2/ SPO11. Sequence comparisons of the 5' flanking regions revealed similar sequence stretches in the respective gene pairs, which may constitute regulatory elements. Similar sequences were also found in the 5' flanking regions of the pairs MSH1/MSH3 and MSH1/MSH6. Upstream of MSH2 three closely spaced sequences similar to UASH elements were found, which - surprisingly are located within the coding region of SPO21. Deletion of these elements resulted in loss of meiotic induction of MSH2. Genetic analysis of homozygous deletion mutants did not reveal any differences from wild type with respect to genetic distance estimates, aberrant segregation, or suppression of homoeologus recombination in an interspecies cross with Saccharomyces paradoxus.