I have been trying to isolate plasmid from BL21. I also used to isolate the plasmid from DH5alpha. But both times i just dont get either the right bands or any plasmid at all. I have used the qiagen kit. Also i am trying to use home made buffers from Molecular cloning book. I follow the protocol to the tee. so i dont understand why i am facing so many problems. please help me!!!!