GAL4 protein activates transcription through binding to upstream activation sequence (UAS), whereas GAL80 protein prevents GAL4-dependent transcription. The temperature-sensitive GAL80[ts] provides a temporal regulation of UAS transgene. For more information on using GAL4/UAS/GAL80, see Duffy (2002): GAL4 System in Drosophila: A Fly Geneticist’s Swiss Army Knife. Genesis 34:1–15.