We have developed a system for temperature-inducible killing of specif
ic cells in the fruitfly Drosophila melanogaster. The system overcomes
many of the limitations of existing cell ablation methods and is in p
rinciple applicable to any non-homeothermic eukaryote. Temperature-sen
sitive and cold-sensitive mutations in the ricin toxin A chain (RTA) o
f castor bean were generated in yeast. One cold-sensitive mutation, RA
cs2, produced temperature-dependent ablation of eye cells in Drosophil
a when expressed under control of the eye-specific sev enhancer. At 29
-degrees-C, cell death was observed within 7 hours in the developing e
ye and no obvious toxic effects were observed elsewhere; at 18-degrees
-C, extremely low toxicity was observed. DNA sequencing of RAcs2 revea
led a single amino acid substitution in the RTA active site cleft.