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-homol ogous genes of the yeast Saccharomyces cerevisiae during the course of meio sis. by quantitative RT-PCR. We found that all mutS homologues (MSH1-6) wer e induced during meiosis, whereas no evidence for regulation of the mutL ho mologues (PMS1, MLH1-3) was obtained. Temporal expression patterns indicati ve of co-regulation were observed for the gene pairs MSH4/MSH5 and MSH2/SPO 11. Sequence comparisons of the 5 ' flanking regions revealed similar seque nce 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 s equences similar to UAS(H) elements were found, which - surprisingly - are located within the coding region of SPO21. Deletion of these elements resul ted in loss of meiotic induction of MSH2. Genetic analysis of homozygous de letion mutants did not reveal any differences from wild type with respect t o genetic distance estimates, aberrant segregation, or suppression of homoe ologus recombination in an interspecies cross with Saccharomyces paradoxus.