Genomic footprinting of the yeast zinc finger protein Rme1p and its roles in repression of the meiotic activator IME1.

The zinc finger protein Rme1p is a negative regulator of the meiotic activator IME1 in Saccharomyces cerevisiae . Prior studies have shown that Rme1p binds in vitro to a site near nt -2030 in the IME1 upstream region, but a genomic mutation in that site has little effect on repression of IME1 . To identify Rme1p binding sites in vivo , we have examined the binding of Rme1p to genomic sites through in vivo footprinting. We show that Rme1p binds to two sites in the IME1 upstream region, near nt -1950 and -2030. Mutations in both binding sites abolish repression of chromosomal IME1 by Rme1p, whereas a mutation in either single site causes partial derepression. Therefore, both Rme1p binding sites are essential for repression of IME1 . Prior studies have shown that repression by Rme1p depends upon RGR1 and SIN4 , which specify RNA polymerase II mediator subunits that are required for normal nucleosome density. We find that RGR1 and SIN4 are not simply required for Rme1p to bind to DNA in vivo . These results suggest that Rme1p functions directly as a repressor of IME1 and that Rgr1p and Sin4p are required for DNA-bound Rme1p to exert repression.