The modified Aedes aegyptii contains two gene cassettes: a fluorescent marker (Discosoma sp. DsRed2) and a sex-specific lethality cassette (Escherichia coli tetracycline-controlled transactivator; tTAV)

Fluorescent marker
Transcription of the fluorescent marker commences from the Autographa californica multiple nucleopolyhedrovirus immediate-early-1 gene promoter and terminates at the Simian vacuolating virus 40 (SV40) poly-adenylation signal. The transcript initially contains a Drosophila melanogaster scraps intron, two synthetic nuclear localization signals (surrounding the DsRed2 sequence) and the Discosoma sp. DsRed2 fluorescent protein. The scraps intron improves mRNA stability and is required for translation of the protein, but is not expected to be included in the translated polypeptide. After splicing and translation, the nuclear localization signals allow DsRed2 to transit and accumulate in the nuclei of cells.

Sex-specific lethality
Transcription of the tTAV commences from the D. melanogaster heat shock protein 70 minimal promoter and terminates at the same SV40 poly-adenylation signal as the other genetic cassette. The transcript contains the Aedes aegypti sex-specific intron, D. melanogaster ubiquitin and tTAV.  In females, splicing removes the sex-specific intron. The remaining transcript is translated to produce a poly-peptide containing ubiquitin and tTAV. Post-translation, ubiquitin is removed, leaving the functional tTAV. Ubiquitin is expected to enhance protein expression within insect cells. In males, splicing occurs from a further downstream site within the sex-specific splicing module. The resulting transcript then contains several stop codons upstream of ubiquitin and tTAV, which disrupt translation and thus prevents the production of the tTAV protein.

Transcriptional expression is also influenced by the tetracycline operator, which is adjacent to the tTAV cassette and acts as a repressible switch. In the presence of tetracycline, tTAV preferentially binds tetracycline rather than the operator sequences. Thus, transcription remains at a basal level and repressed. In the absence of tetracycline, tTAV binds the operator sequences and stimulates transcription, resulting in elevated levels of the tTAV protein.