The P{CoinFLP-longGMR-GAL4} construct contains "longGMR" regulatory sequences that are separated from the GAL4 coding region by a disruptive sequence cassette. The disruptive cassette contains a transcriptional STOP sequence plus two pairs of mutually incompatible FRT sites (FRT and FRT3) which are arranged such that a single FLP-mediated recombination event, excising either the FRT-flanked sequence or the FRT3-flanked sequence can occur in a stochastic manner, with no further recombination possible. If excision of the FRT3-flanked sequence occurs, the STOP sequence is still present and GAL4 is not expressed, while excision of the FRT-flanked sequence removes the STOP cassette, allowing GAL4 expression under the control of the longGMR regulatory sequences.