Selection and characterization of a glucokinase-deficient mutant of Tetrahymena thermophila.

We have isolated a mutant of Tetrahymena thermophila that is resistant to inhibition of growth by the glucose analog 2-deoxyglucose. The mutant exhibits a deficiency in a cytoplasmic glucokinase. This enzymatic defect and the attendant inability to convert 2-deoxyglucose to toxic phosphorylated derivatives is apparently the sole basis for the mutant phenotype since transport of glucose and 2-deoxyglucose is unimpaired; there is no elevation of glucose-6-phosphatase activity, which could decrease the level of toxic 2-deoxyglucose metabolites. Genetic analyses have shown that the mutant allele is recessive and inherited as a single Mendelian mutation. The glucokinase-deficient strain described here is useful for the selection of other mutants in this organism and for the investigation of various cellular processes initiated or modulated by glucose and its analogs. We have exploited the molecular defect in this strain to investigate the initial steps in the cyclic AMP-mediated repression of galactokinase gene expression which is caused by glucose.