FUNCTIONAL AND CONSERVED DOMAINS OF THE DROSOPHILA TRANSCRIPTION FACTOR ENCODED BY THE SEGMENTATION GENE KNIRPS

The Drosophila gap gene knirps (kni) is required for abdominal segment ation. It encodes a steroid/thyroid orphan receptor-type transcription factor which is distributed in a broad band of nuclei in the posterio r region of the blastoderm. To identify essential domains of the kni p rotein (KNI), we cloned and sequenced the DNA encompassing the coding region of nine kni mutant alleles of different strength and kni-homolo gous genes of related insect species. We also examined in vitro-modifi ed versions of KNI in various assay systems both in vitro and in tissu e culture. The results show that KNI contains several functional domai ns which are arranged in a modular fashion. The N-terminal 185-amino-a cid region which includes the DNA-binding domain and a functional nucl ear location signal fails to provide kni activity to the embryo. Howev er, a truncated KNI protein that contains additional 47 amino acids ex erts rather strong kni activity which is functionally defined by a wea k kni mutant phenotype of the embryo. The additional 47-amino-acid str etch includes a transcriptional repressor domain which acts in the con text of a heterologous DNA-binding domain of the yeast transcriptional activator GAL4. The different domains of KNI as defined by functional studies are conserved during insect evolution.