UME6 IS A CENTRAL COMPONENT OF A DEVELOPMENTAL REGULATORY SWITCH CONTROLLING MEIOSIS-SPECIFIC GENE-EXPRESSION

The UME6 gene of Saccharomyces cerevisiae was identified as a mitotic repressor of early meiosis-specific gene expression, It encodes a Zn(2 )Cys(6) DNA-binding protein which binds to URS1, a promoter element ne eded for both mitotic repression and meiotic induction of early meioti c genes, This paper demonstrates that a complete deletion of UME6 caus es not only vegetative derepression of early meiotic genes during vege tative growth but also a significant reduction in induction of meiosis -specific genes, accompanied by a severe defect in meiotic progression . After initiating premeiotic DNA synthesis the vast majority of cells (approximate to 85%) become arrested in prophase and fail to execute recombination; a minority of cells (approximate to 15%) complete recom bination and meiosis I, and half of these form asci, Quantitative anal ysis of the same early meiotic transcripts that are vegetatively derep ressed in the ume6 mutant, SPO11, SPO13, IME2, and SPO1, indicates a l ow level of induction in meiosis above their vegetative derepressed le vels, In addition, the expression of later meiotic transcripts, SPS2 a nd DIT1, is significantly delayed and reduced, The expression pattern of early meiotic genes in ume6-deleted cells is strikingly similar to that of early meiotic genes with promoter mutations in URS1, These res ults support the view that UME6 and URS1 are part of a developmental s witch that controls both vegetative repression and meiotic induction o f meiosis-specific genes.