Fig 1. Conditional Misexpression Transactivation permits the expression of any gene in any pattern. The enhancer trap systems employed by the project both contain a gene encoding a trans-acting transcriptional activator under the control of a minimal promoter. When insertion brings the minimal promoter under the influence of an enhancer, or other controlling sequence, this dictates the pattern of transcription of the trans-activator gene. The product of this gene, namely GAL4 or LhG4, can then bind to its recognition site (UAS or pOp6 respectively) and activate transcription of the reporter gene, revealing the pattern of expression dictated by the controlling sequence. Any transgene under the control of the relevant transactivator binding site can then be introduced to into a specific enhancer-trap line and expressed in the same tissue and temporal specific pattern as the reporter gene. For each system a second population of transformed plants is created with random insertions of the trans-activation binding site in the background of an inducible GAL4 or LhG4 source. Activation tagged insertions, pre-selected for a conditional dominant phenotype can be crossed into selected enhancer-trap lines to restrict expression to specific spatial and temporal patterns.
