A sequence cassette encoding the 364bp Wari insulator plus an FRT cassette that contains mini-y sequence has been inserted into the attP site present in the TI{TI}w-ΔWari insertion present on the wΔWari-spB chromosome. The mini-y sequence is not expressed (it is not known whether it is silenced because of a position effect or whether a lesion has been introduced into the y sequence).