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Dear all: I would like to seek your wisdom on our latest diffraction pattern. We have been working on protein/DNA complex. The protein and DNA have similar MW. By binding assay, we know the minimal length of DNA. (The Kd is 0.1-1 microMolar and we can see the complex formation in size exclusion chromatography up to 200mM NaCl but also some unbound form) After trying different length of DNA, we recently obtained many crystal hits (the percipient is either PEG400 or MPD). The final ratio (prior to protein crystallization) between protein and DNA is 1:1.6 considering some loss of protein during concentration. The crystal is birefringent. Since high conc. of PEG400 (MPD), the crystals were directly frozen in liquid N2. However, crystals only diffract to 8-10 angstrom (anisotropic) and also weird striking line are present (please see attachment). Do you think if it is DNA alone crystal or protein/DNA complex crystal? How should I improve the diffraction quality? PS. We have done some tests. For example, set up the same conditions with DNA alone. I also tried to dissolve crystals in Bradford assay solution and I believe I saw some blueish color. But none of these tests are conclusive. Thanks for your suggestion. Joseph