RPH1 and GIS1 Are Damage-Responsive Repressors of PHR1

The Saccharomyces cerevisiae DNA repair gene PHR1 encodes a photolyase that catalyzes the light-dependent repair of pyrimidine dimers. PHR1 expression is induced at the level of transcription by a variety of DNA-damaging agents. The primary regulator of the PHR1 damage response is a 39-bp sequence called URS(PHR1) which is the binding site for a protein(s) that constitutes the damage-responsive repressor PRP. In this communication, we report the identification of two proteins, Rph1p and Gis1p, that regulate PHR1 expression through URS(PHR1). Both proteins contain two putative zinc fingers that are identical throughout the DNA binding region, and deletion of both RPH1 and GIS1 is required to fully derepress PHR1 in the absence of damage. Derepression of PHR1 increases the rate and extent of photoreactivation in vivo, demonstrating that the damage response of PHR1 enhances cellular repair capacity. In vitro footprinting and binding competition studies indicate that the sequence AG(4) (C(4)T) within URS(PHR1) is the binding site for Rph1p and Gis1p and suggests that at least one additional DNA binding component is present in the PRP complex.