Genetic and developmental analysis of mutant Ketel alleles that identify the Drosophila importin-beta homologue.

The Ketel gene of Drosophila melanogaster was identified by four KetelD dominant female-sterile mutations and their 27 revertants. The X-ray and the P-induced KetelR alleles delineated the Ketel locus to the 38E1.2-3 cytological position. Although oogenesis proceeds, normally in the KetelD/+ females, embryogenesis comes to a deadlock shortly after fertilization inside the normal-looking eggs of the KetelD/+ females. The KetelD alleles are dominant negative mutations of antimorph type. Cytoplasm of the KetelD/(+)-derived eggs induce lesions when injected into wild-type eggs and the KetelD alleles can be reverted. Zygotes homozygous for loss-of-function (revertant) KetelR alleles die in second larval instar. Analysis of the cold-sensitive Ketel alleles and the genetic interactions between importin-alpha and KetelR mutant alleles indicate an involvement of the Ketel gene product in oo-, embryogenesis and larval life and show interaction of the KETEL protein with different components of nuclear processes. Molecular analysis (to be published elsewhere) confirmed the genetic data and revealed that the Ketel gene encodes the Drosophila homologue of importin-beta, an essential component of nuclear protein import.