The vestigial gene (vg(+)) is required for normal wing development and
is expressed in a spatially distinct pattern in imaginal discs. We ha
ve exploited a general property of P element alleles to target an enha
ncer trap to the 5' region of the gene. By replacing the P element res
ident at this site in vg(21) with a P element carrying a lacZ reporter
gene, the vg(lacZ1) allele was selected on the basis of its increased
mutant phenotype. In contrast to vg(+) expression, which occurs prima
rily in the presumptive wing margin and hinge, beta-galactosidase expr
ession in vg(lacZ1) wing discs is localized to the dorsal wing surface
and displays homologous haltere expression. The targeting of P elemen
t enhancer traps could be readily extended to other genes with low rat
es of primary P element insertion. (C) 1994 Academic Press, Inc.