Mi{DH.2} contains a 'Double Header' (DH) cassette designed to efficiently trap genes when inserted in a codon phase 2 coding intron. The DH cassette comprises two independent trapping modules oriented in opposite directions: 1. a protein-trap (PT) module for tagging endogenous proteins, composed of a splice acceptor site, a EGFP-Tag:CALI(TC)-Tag:StrepII-Tag:CS(TEVp)-3xTag:FLAG multi-tag cassette and a splice donor site, and 2: a gene-trap (GT) module designed to truncate the endogenous gene into which it inserts, as it contains T2A-GAL4 followed by a polyadenylation signal. Translation should skip at the T2A sequence, truncating the endogenous protein and producing a separate GAL4 protein. Both of the modules are in codon phase 2. Mi{DH.2} is generated in vivo by using a donor transgene or plasmid, in which the DH cassette containing the two trapping modules is flanked by inverted attB sites, to replace the RMCE cassette present in a Mi{MIC} element insertion in a coding intron. Depending on the orientation in which the DH cassette is inserted relative to the direction of transcription of the endogenous gene, the inserted Mi{DH.2} element can either be in the 'protein-trap' or 'gene-trap' orientation for that gene.