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co-eluted protein with his-tag protein - (Jul/24/2012 )

I have recently expressed a protein in BL21, about 31 kDa with Histag (Flexi system, Promega). I tried to purify the protein using MagneHis Protein Purification System (Promega). I find that my elute contains most protein in the host cell. I’ve tried increasing the NaCl conc in the wash buffer, but the problem still exists.
Any suggestion what’s happening? Thanks for help.


did you check if your protein of interest was really overexpressed? If so, was it prominent in the elutions?

-Inmost sun-