Contains the w+mC minigene, with a dimer of a 227bp sequence containing a mutated scs' D (high-affinity) site (the three CGATA motifs have been mutated to CTCGA) inserted 5' of the minigene (the spacing between the two D sites is the same as that found between the D site and lower affinity B site in scs') and a 990bp PvuII scs fragment inserted 3' of the minigene.