Schematic of pPSU1 and pPSU2 Plasmids (IMAGE) Penn State Caption This is a schematic of pPSU1 and pPSU2 plasmids. The 1000-base-pair (1 kb) ladder is made by cutting the two plasmids with the restriction enzyme, EcoRV. The 100-base-pair (bp) ladder is made by cutting the plasmids with PstI. Credit Penn State University Usage Restrictions The image credit must be published with the image. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.