pMD20 and pMD19 (Simple) T-Vectors are linearized PCR cloning vectors (cleaved by EcoRV) with single 3’-terminal thymidine residues (dT) at both ends. These T-overhangs at the cloning site improve the efficiency of ligation of PCR products that contain dA-overhangs. The inclusion of lacZ in these vectors allows blue/white screening for the detection of successful ligations.