A 3.8Kb upstream regulatory fragment and 2.0kb downstream regulatory sequence fragment from gbb are cloned around a gbb coding sequence containing a mutation in the S1 cleavage consensus site.
The presence of gbbt.mS1 partially rescues the lethality associated with gbb1 mutants, with 7.4% of embryos surviving to adulthood. These flies exhibit defective wings. Wings from adult survivors show blistered and ectopic venation phenotypes.