Mutated Fab-7 boundary element sequence has been inserted into the attP site present in TI{TI}Fab-7attP50, reconstituting a mutant Fab-7 element that that contains mutations in all six GAGA motifs in the HS1 nuclease-hypersensitive region, plus mutations in two GAGAA motifs. A loxP site and an FRT site are present downstream of the inserted sequence.