The COT] gene of Saccharomyces cerevisiae has been isolated as a dosage-dependent suppressor of cobalt toxicity. Overexpression (10,13,27). Although the CUP1 protein has been shown to bind several metals (64), increased expression of the CUP1 gene confers tolerance only to copper and cadmium (27, 30).We describe the isolation of COT1, a gene that when overexpressed enables wild-type strains of S. cerevisae to grow in media containing as much as 20 mM CoCl2. Deletion of the COTI gene makes cells more sensitive to cobalt than are wild-type strains. Since COT) also affects cobalt transport in a dosage-dependent manner, COT) appears to be involved in both the accumulation and detoxification of Co2+ ions. 3678on May 11, 2018 by guest