GENETIC AND DEVELOPMENTAL ANALYSIS OF MUTANT KETEL ALLELES THAT IDENTIFY THAT DROSOPHILA IMPORTIN-BETA HOMOLOG

The Ketel gene of Drosophila melanogaster was identified by four Ketel (D) dominant female-sterile mutations and their 27 revertants. The X-r ay and the P-induced Ketel(R) alleles delineated the Ketel locus to th e 3BE1.2-3 cytological position. Although oogenesis proceeds normally in the Ketel(D)/+ females, embryogenesis comes to a deadlock shortly a fter fertilization inside the normal-looking eggs of the Ketel(D)/+ fe males. The Ketel(D) alleles are dominant negative mutations of antimor ph type. Cytoplasm of the Ketal(D)/+-derived eggs induce lesions when injected into wild-type eggs and the Ketel(D) alleles can be reverted. Zygotes homozygous for loss-of-function (revertant) Ketel(R) alleles die in second larval instar. Analysis of the cold-sensitive Ketel alle les and the genetic interactions between importin-alpha and Ketel(R) m utant alleles indicate an involvement of the Ketel gene product in oo- , embryogenesis and larval life and show interaction of the KETEL prot ein with different components of nuclear processes. Molecular analysis (to be published elsewhere) confirmed the genetic data and revealed t hat the Ketel gene encodes the Drosophila homologue of importin-beta, an essential component of nuclear protein import.