double-time is identical to discs overgrown, which is required for cell survival, proliferation and growth arrest in Drosophila imaginal discs

We have isolated the discs overgrown gene of Drosophila and shown that it e ncodes a homolog of the Casein kinase I delta/epsilon subfamily and is iden tical to the double-time gene. However, in contrast to the weak double-time alleles, which appear to affect only the circadian rhythm, discs overgrown alleles, including bona fide null alleles, show strong effects on cell sur vival and growth control in imaginal discs. Analysis of their phenotypes an d molecular lesions suggests that the Discs overgrown protein is a crucial component in the mechanism that links cell survival during proliferation to growth arrest in imaginal discs. This work provides the first analysis in a multicellular organism of Casein kinase I delta/epsilon functions necessa ry for survival. Since the amino acid sequences and three-dimensional struc tures of Casein kinase I delta/epsilon enzymes are highly conserved, the re sults suggest that these proteins may also function in controlling cell gro wth and survival in other organisms.