Sequence encoding GAL4 has been inserted into the attP site present in TI{TI}otpKO, resulting in a chromosome in which GAL4 is inserted in place of a 64bp deletion that extends from 11bp upstream of the ATG codon in otp exon 2 through to the beginning of the next intron (removes the exon 2 donor splice). A single loxP site is present downstream of the GAL4 coding sequence.