The snRNA:U6:96Ac promoter drives expression of a polycistronic tRNA-gRNA cassette that encodes two sgRNAs, 'gRNA#1' (sequence GTAGTACGATCATAACAACG) and 'gRNA#2' (sequence GTACATCCATACAGTACCAG), both of which have no target site in the wild-type D. melanogaster genome.