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Seeing the diffuse streaking threads that have cropped up recently got me to thinking about many of the DNA data sets we have collected on. We always see diffuse streaking along lattice lines. See images: http://vespa.chem.umd.edu/~paul/hex_streak01.png http://vespa.chem.umd.edu/~paul/hex_streak02.png http://vespa.chem.umd.edu/~paul/hex_streak03.png My original interpretation of this as fiber diffraction from alignment of DNA bases came after reading Doucet et al. Nature 337, 190-192 and seeing that the streaks start at around 3.4A and orientation of the helical portions of the structure are perpendicular to the six-fold. I didn't really give it much more thought till seeing the threads about diffuse streaking. These show up even in crystals that diffract to higher resolution than the one shown in the images. I wonder if this is actually something else given that they are along lattice lines? Opinions? --paul