The piB-GFP plasmid contains a recombination-mediated cassette exchange (RMCE) cassette that consists of two inverted attB sites which surround an enhancer trap cassette composed of a minimal Hsp70 promoter, the EGFP reporter and an SV40 tail. In the presence of phiC31:int integrase, the attB cassette can undergo RMCE with a target in the genome that contains inverted attP sites, replacing the target attP cassette with the donor attB cassette sequence.