Coupling of Saccharomyces cerevisiae early meiotic gene expression to DNA replication depends upon RPD3 and SIN3

It has been established that meiotic recombination and chromosome segregati on are inhibited when meiotic DNA replication is blocked. Here we demonstra te that early meiotic gene (EMG) expression is also inhibited by a block in replication. Since early meiotic genes are required to promote meiotic rec ombination and DNA division, the low expression of these genes may contribu te to the block in meiotic progression. We have identified three Hur(-) (HU reduced recombination) mutants that fail to couple meiotic recombination a nd gene expression with replication. One of these mutations is in RPD3, a g ene required to maintain meiotic gene repression in mitotic cells. Complete deletions of RPD3 and the repression adapter SIN3 permitted recombination and early meiotic gene expression when replication was inhibited with hydro xyurea (HU). Biochemical analysis showed that the Rpd3p-Sin3p-Ume6p repress ion complex does exist in meiotic cells. These observations suggest that re pression of early meiotic genes by SIN3 and RPD3 is critical for the normal response to inhibited replication. A second response to inhibited replicat ion has also been discovered. HU-inhibited replication reduced the accumula tion of phospho-Ume6p in meiotic cells. Phosphorylation of Ume6p normally p romotes interaction xith the meiotic activator Ime1p, thereby activating ER ;IG expression. Thus, inhibited replication may also reduce the Ume6p-depen dent activation of EMGs. Taken together, our data suggest that both active repression and reduced activation combine to inhibit Eh le expression when replication is inhibited.