Summary: Thirty Ca-sensitive (: cium ensitive) mutants of were isolated by replica-plating. These mutants, which each had a single recessive chromosomal mutation, were divided into 18 complementation groups. Some mutants showed a phenotype of specific sensitivity to Ca, while others showed phenotypes of sensitivities to several divalent cations. From measurements of the calcium contents and initial rates of Ca uptake of the mutants, 16 of the 18 complementation groups were classified into four types: type I mutants (, and ) had both elevated calcium contents and increased uptake activities. A type II mutant () had a normal calcium content and normal uptake activity; type III mutants ( and ) had elevated calcium contents but normal initial rates of Ca uptake; type IV mutants ( and ) had normal calcium contents but increased initial rates of Ca uptake. Two of the mutants ( and ) had intermediate biochemical properties. The primary defects of these four types of mutants were considered in terms of the Ca transport system(s). Both type I and type III mutants, which had elevated calcium contents, simultaneously showed a trifluoperazine-sensitive phenotype, suggesting a close correlation of this phenotype with elevated calcium content. In addition, all type IV mutants were unable to utilize nonfermentable sugars. One gene, , was located on the left arm of chromosome V.


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