Hello There! Here are a couple of quick thoughts in response to your question, none of which will fully resolve your concern:
(1) Wash your crystals, crush them, add native gel loading dye and run a native gel. First stain with ethidium bromide, then stain with coomassie blue. If you stain for both DNA and protein, that suggests you may have protein-DNA complex in the crystal. I know a lot of people use dyes like Izit (I don't use this approach!) that are used to stain crystals to detect protein. (2) Capture a few diffraction images, if possible. Generally there will be a DNA fibre diffraction pattern on the diffraction image for a crystal containing DNA but obviously that doesn't suggest presence or absence of protein. Is the unit cell estimate much larger than can be expected for DNA alone (unless you are unlucky enough that your DNA fragment will pack in a way to form a large unit cell)? Ultimately, the sure shot way is to get decent enough crystals to collect datasets and solve the structure to discover if the electron density has "room" to build a model with both protein and DNA. Cheers and good luck! Raji On Thu, Jan 9, 2014 at 9:13 AM, Acoot Brett <[email protected]> wrote: > Dear All, > > I am now working on the crystallization of a complex of protein-16 bp DNA > by co-crystallization. In the screening very small needle-like crystal > occurs. If not salt crystal, is there a method to know it is not the > crystal of the DNA? > > Cheers, > > Acoot > -- Raji Edayathumangalam Instructor in Neurology, Harvard Medical School Research Associate, Brigham and Women's Hospital Visiting Research Scholar, Brandeis University
