Structure-specific recognition proteins (SSRPs) bind to DNA containing intrastrand cross-links formed by the anticancer drug cisplatin. A yeast gene encoding an SSRP, designated IXR1, was cloned and sequenced. The Ixr1 protein, a member of the high mobility group-box protein family, bound specifically to DNA modified with cisplatin but not inactive platinum compounds. A yeast strain with an inactivated IXR1 gene was half as sensitive to cisplatin and accumulated one-third as many platinum-DNA lesions after treatment with cisplatin as the parental strain. These findings suggest that SSRPs play a role in mediating the cytotoxicity of cisplatin.