[Construction of pEGFP-C1/U6-mediated plasmid expressing MDR1 shRNA].

To construct a plasmid expressing MDR1 short hairpin RNA (shRNA) mediated by pEGFP-C1/U6 vector, two coding sequences of 19 nucleotides were selected from MDR. Two pairs of oligonucleotides were designed for these two fragments. After annealing the formed double-stranded DNAs were ligated with plasmid pEGFP-C1/U6 (pEGFP-C1 vector with U6 promoter). The plasmids producing MDR1 shRNA were constructed from the inverted motif containing 9 spacers and four Ts. The results showed that the constructed plasmids were named pEGFP-C1/U6/A and pEGFP-C1/U6/B, and the constructs were identified by restriction and sequence analysis, no any base mutation was observed. It is concluded that plasmids of pEGFP-C1/U6/A and pEGFP-C1/U6/B expressing MDR1 shRNA were successfully constructed, providing a highly effective method for reversing the multidrug resistance in clinic.