THE SUPPRESSOR OF FUSED GENE ENCODES A NOVEL PEST PROTEIN INVOLVED INDROSOPHILA SEGMENT POLARITY ESTABLISHMENT

Suppressor of fused, Su(fu), was identified as a semi-dominant suppres sor of the putative serine/threonine kinase encoded by the segment pol arity gene fused in Drosophila melanogaster. The amorphic Sw(fu) mutat ion is viable, shows a maternal effect and displays no phenotype by it self. Su(fu) mutations are often found associated to karmoisin (kar) m utations but two complementation groups can be clearly identified. By using a differential hybridization screening method, we have cloned th e Su(fu) region and identified chromosomal rearrangements associated w ith Su(fu) mutations. Two classes of cDNAs with Similar developmental patterns, including a maternal contribution, are detectable in the reg ion. Transformation experiments clearly assigned the Su(fu)(+) functio n to one of these transcription units while the other one can be most likely assigned to the kar(+) function. Surprisingly the 5' end of the kar RNA mapped within the 3' untranslated region of the Su(fu) transc ribed sequence. The Su(fu) gene encodes a 53-kD protein, which contain s a PEST sequence and shows no significant homologies with known prote ins. Genetic analysis shows that proper development requires a fine tu ning of the genetic doses of fu and Su(fu) both maternally and zygotic ally. These results, together with previous genetic and molecular data , suggest that fused and Suppressor of fused could act through a compe titive posttraductionnal modification of a common target in the hedgeh og signaling pathway.