Tubulin regulatory sequences drive expression of a dicistronic transcript that encodes two open reading frames separated by a self-cleaving P2A sequence (this results in separate translation of each protein). The first ORF encodes Scer\GAL3, the second ORF encodes GAL80. In the presence of galactose, the Scer\GAL3 protein has high affinity for GAL80, sequestering the GAL80 protein and preventing it from repressing GAL4-driven expression.