Construction of retroviral siRNA delivery vector Schematic of genome structure. All plasmids were derived from pMSCVpuro (Clontech). The inserted U6 promoter is illustrated in blue, while the control and anti-NDR hairpins are shown in red and green, respectively. Ψ+, extended packaging signal. MCS, multiple cloning site. PGK, murine phosphoglycerate kinase promoter. Puror, puromycin resistance gene. N/B and B/N, cloning junction generated by ligating the blunt ended BamHI and NsiI restriction sites.