What troubleshooting would you perform on a his-tagged E. coli protein that crashes out during the wash step of a batch Ni purification?

Bound clarified lysate for 1hr @ 4C in 150mM Tris, 50mM NaCl, 40mM Imidazole. Then spun down, and when I added the same buffer to wash, the protein crashed out (lots of white gunk & precipitate)....

02 February 2013 240 17 View