Division of Molecular Genetics, University of Glasgow, Church street, Glasgow G11 5JS, UK.,
We have found two P[GAL4] lines (c232 and c507) with an identical GAL4-directed expression pattern in the ellipsoid body of the brain and in the Malpighian (renal) tubules in the abdomen. Both P elements map to the same chromosomal site (100B). The locus has now been cloned by plasmid rescue. Restriction mapping and DNA sequencing reveal the two P[GAL4] elements to be inserted only 46 bp apart, and in opposite orientations. Three flanking genes have been identified. Calcineurin A1 lies to one side, and two very closely linked genes lie to other. The nearest of the latter encodes an alkaline phosphatase; the more distant gene has yet to be matched to any known sequence, but has markedly head-elevated expression. In situ hybridisation to tissue sections reveals the alkaline phosphatase gene to have an identical expression pattern to the enhancer-trap pattern. Both insertions are homozygous viable, and there are no other obvious defects. In order to generate loss-of function allelese, imprecise P-element excision has been carried out. The mutants are currently being analysed.