I have been trying to crystallize protein DNA complex, but all the time i end up with DNA crystals. Even i changed the length of DNA many times but still no complex, DNA only crystallizes! Does anybody has idea, why do DNA crystallize by itself ? My protein behaves very nicely, Dynamic Light Scattering always shows nice values implies homogenous but once i tried to ran acidic native page but it shows little bit aggregated. The protein is highly hydrophilic and soluble, and has only three cysteines, is it there any possibility of aggregation due to cysteine, when overexpressed in E.coli ? and one more thing i mixed protein and DNA together and ran agarose gel to see any gel shift, indeed there is a binding, but when i take the same thing to set drops, only DNA crystals. Kindly suggest me, what could be done.