protein purification problem - DNA stuck to protein problem (Sep/28/2004 )
I am having a HUGE problem purifying a mutant of my protein that forms multimers upon cell lysis (8-10mers of the protein as soon as I sonicate the cells). There is a LOT of DNA stuck to it and I can't seem to get rid of it either with DNAse I or polyethylinimine (the protein precipitates with the DNA) or even with purification steps (Ni-NTA column); it seems to be stuck even with 2M salt!?! What do I do? I grow the cells at 37 C for 4-5 hrs and at 30C after induction. Should I simply lower the growth temp to 15C after induction? Any ideas would be greatly appreciated!