MOLECULAR CHARACTERIZATION OF THE LETHAL OF SCUTE GENETIC FUNCTION

The lethal of scute (l'sc) genetic function, which plays an essential role in the early development of the central nervous system of the Dro sophila embryo, is localized within the achaete-scute complex (AS-C). Several lines of evidence have suggested that the AS-C T3 transcriptio n unit corresponds to the l'sc function. We demonstrate that short fra gments of DNA, containing the T3 transcribed region and a few kilobase s of flanking sequences, rescue, albeit partially, the lethality and n eural phenotype of l'sc deletions. Still, the complex wild-type patter n of expression of T3 is not reproduced by the transduced genes. This depends on cis-control elements scattered within the entire AS-C DNA a nd intermingled with regulatory elements specific for other AS-C trans cription units. These elements are necessary for the initial activatio n of T3 in the neuroectoderm, probably mediated by axis-patterning gen es. The presence of a cluster of F-boxes, upstream of the T3 transcrib ed region, suggests another level of control of T3 expression by basic -helix-loop-helix proteins, among them its own gene product.