No mutation has been detected in the P{P-Sal} element, but the mutant phenotype in this line (P\TSal-M20 shows loss of silencing of P{lacW}ciDplac compared to its P\TSal progenitor) maps to within 0.27cM from the P{P-Sal}Pak3P-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.