ISOLATION OF TEMPERATURE-SENSITIVE DIPHTHERIA TOXINS IN YEAST AND THEIR EFFECTS ON DROSOPHILA CELLS

We have isolated temperature-sensitive diphtheria toxins (DT-A(ts)) to develop a method that allows temporal impedement of cellular function s. Four DT-A(ts) genes were isolated in a mutagenesis screen using the yeast, Saccharomyces cerevisiae. When expressed in yeast, these DT-A( ts) arrest growth at 18-degrees-C but not at 30-degrees-C. Three DT-A( ts) were subsequently tested in the R1-R6 photoreceptor cells of trans genic fruit flies, Drosophila melanogaster. The toxins show similar te mperature dependence in both organisms, suggesting that they may be us eful in a wide range of non-homeothermic species. DNA sequence analysi s revealed that three of the four DT-A(ts) mutations are novel. Intere stingly, the fourth DT-A(ts) carries the same point mutation as the ex tensively characterized CRM197, an ADP ribosyltransferase-defective fo rm of diphtheria toxin.