The snRNA:U6:96Ac promoter is separated from four gRNAs (each with an attP site upstream of the gRNA) by an attB site and a Disc\RFP3xP3.PB marker. In the absence of phiC31:int, the Disc\RFP3xP3.PB marker prevents expression of the gRNAs. In the presence of phiC31:int, the attB site can recombine stochastically with any of the four attP sites upstream of a gRNA, removing the marker, creating an attR site and allowing expression of a single gRNA (the one immediately downstream of the attR site). Each of the gRNAs targets a different region of the Tag:M(mCd8a) tag.