This vector can silence the expression of 2 genes simultaneously. Sequences from the target genes are used to design short cDNAs that are ligated into the insertion sites at each end of the promoter. The cDNAs are constructed by annealing compementary oligonucleotides to one another. Each oligonucleotide is designed with a 4-base overhang at its 5'-end. The overhangs complement vector sequences that remain after digestion with a pair of restriction enzymes that is unique for each insertion site. The neomycin resistance marker facilitates the creation of stable cell lines.