Abstract
The Drosophila abelson (abl) gene encodes the homolog of the mammalian c-abl cytoplasmic tyrosine kinase and is an essential gene for the development of viable adult flies. Three second-site mutations that suppress the lethality caused by the absence of abl function have been isolated, and all three map to the gene enabled (ena). The mutations are recessive embryonic lethal mutations but act as dominant mutations to compensate for the neural defects of abl mutants. Thus, mutations in a specific gene can compensate for the absence of a tyrosine kinase.
