While the interior of a protein resembles a crystal in terms of atomic packing density, it is certainly not crystalline, as it lacks the crucial requirement of being arranged in a regular pattern.
You need a regular crystal lattice in order to amplify x-ray diffraction signals to detect them.
That's why the resolution on this is so bad compared to x-ray crystallography studies. However, since you don't need crystals, this can be very useful for larger complexes and stuff, though probably not single proteins (unless the resolutions comes up 2 orders of magnitude).
Slashdot Mirror
While the interior of a protein resembles a crystal in terms of atomic packing density, it is certainly not crystalline, as it lacks the crucial requirement of being arranged in a regular pattern. You need a regular crystal lattice in order to amplify x-ray diffraction signals to detect them. That's why the resolution on this is so bad compared to x-ray crystallography studies. However, since you don't need crystals, this can be very useful for larger complexes and stuff, though probably not single proteins (unless the resolutions comes up 2 orders of magnitude).
No, you'd only find "I" in RNA computing http://en.wikipedia.org/wiki/Inosine