I set up the crystallization of protein-DNA complex for initial screen and found the condition to optimize (0.1M HEPES pH6.5, 0.2MgCl2, 25% PEG3350). After rounds of optimization, the quality of crystals got promoted but still cannot reach the perfect status. I have confined the proper range of pH, precipitant concentration. Over 80% crystals display round or twin-crystals only 20% showed diamond shape or sharp-edged crystals.
I also added 96 additives for screening but it didn't show obvious improvement. How can I furtherly improve the crystal quality?