The pBS-KS-attB1-2-GT-SA-GAL4-Hsp70pA plasmid contains a recombination-mediated cassette exchange (RMCE) cassette that consists of two inverted attB sites which surround a mutagenic gene trap cassette composed of a splice acceptor site, the GAL4 coding sequence and a Hsp70 polyadenylation signal. In the presence of phiC31:int integrase, the attB cassette can undergo RMCE with a target in the genome that contains inverted attP sites, such as the Mi{MIC} element, replacing the target attP cassette with the donor attB cassette sequence.