The stoned gene of Drosophila metanoguster is required for normal neuronal function in both adult and larva. We have identified DNA sequences that lie within a genetic region that is known to include the stoned gene and that also reveal restriction site variations in two stoned lethal mutants. This genomic region contains a single transcription unit coding for an ~8.4-kb transcript. The transcript is preferentially expressed in the head of adult flies. The isolation and sequencing of cDNA and genomic clones reveals that stoned appears to encode a dicistronic mRNA, although the possible existence of other forms of mRNA cannot be excluded. Antibody cross-reactivity shows that two proteins are translated from the stoned locus in vivo. Both open reading frames (ORFs) encode novel proteins. The protein encoded by the first ORF contains four tandemly repeated motifs, and one domain of the protein encoded by the second OW shows similarity to a family of proteins (AP50s) associated with clathrin assembly protein complexes.

The genetic complementation patterns of both behavioral and lethal alleles at the stoned locus have been characterized. Mosaic analysis of a stoned lethal allele suggests that stoned functions either in the nervous system or in both the nervous system and musculature, but is not required for gross neural development. The behavioral alleles stnts and stnC, appear to be defective in a diametrically opposite sense, show interallelic complementation, and indicate distinct roles for the stoned gene product in the visual system and in motor coordination. A number of other neurological mutations have been investigated for their possible interaction with the viable stoned alleles. Mutations at two loci, dunce and shibire, act synergistically with the stnts mutations to cause lethality, but fail to interact with stnC. A third variant (Suppressor of stoned) has been identified which can suppress the debilitation associated with the stnts mutations. These data, together with a previously identified interaction between the stnts and tan mutants, indicate a central role for the stoned gene product in neuronal function, and suggests that the stoned gene product interacts, either directly or indirectly, with the neural cAMP second messenger system, with the synaptic membrane recycling pathway via dynamin, and with biogenic amine metabolism.

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