Am trying to digest PET 22b with BamH1 and Xho1, however, I met repeated failure with incomplete digestion. I tried various tricks like increase or decrease the total volume reaction, concentration of the enzyme, etc with no success. I believe there might be some contamination with my plasmid DNA that might be preventing it from complete digestion, but I have no idea what that might be. I am using DH5a to grow the PET vector and Zyppy plasmid mini prep kit for plasmid isolation. The quality of enzymes are good as other members in our lab use the same enzymes for other purposes. I'm sick of trying all alternatives and lastly I resort to post it here for need of help. I hope masters in Cloning will help me to solve my issue....Thanks in advance for all valuable suggestions.