SPALT ENCODES AN EVOLUTIONARILY CONSERVED ZINC-FINGER PROTEIN OF NOVEL STRUCTURE WHICH PROVIDES HOMEOTIC GENE-FUNCTION IN THE HEAD AND TAILREGION OF THE DROSOPHILA EMBRYO

The region specific homeotic gene spalt (sal) of Drosophila melanogast er promotes the specification of terminal pattern elements as opposed to segments in the trunk. Our results show that the previously reporte d sal transcription unit was misidentified. Based on P-element mediate d germ line transformation and DNA sequence analysis of sal mutant all eles, we identified the transcription unit that carries sal function. sal is located close to the misidentified transcription unit, and it i s expressed in similar temporal and spatial patterns during embryogene sis. The sal gene encodes a zinc finger protein of novel structure com posed of three widely spaced 'double zinc finger' moths of internally conserved sequences and a single zinc finger moth of different sequenc e. Antibodies produced against the sal protein show that sal is first expressed at the blastoderm stage and later in restricted areas of the embryonic nervous system as well as in the developing trachea. The an tibodies detect sal homologous proteins in corresponding spatial and t emporal patterns in the embryos of related insect species. Sequence an alysis of the sal gene of Drosophila virilis, a species which is phylo genetically separated by similar to 60 million years, suggests that th e sal function is conserved during evolution, consistent with its prop osed role in head formation during arthropod evolution.