No mutation has been detected in the P{P-Sal} element, but the mutant phenotype in this line (P\T^Sal-M20 shows loss of silencing of P{lacW}ci^Dplac compared to its P\T^Sal progenitor) maps to within 0.27cM from the P{P-Sal}Pak3^P-Sal progenitor insertion. There may therefore be a mutation in a nearby enhancer sequence that controls Pak3 and thereby regulates the expression of the P-element repressor coding sequence via the gene-trapped P-element promoter.