There is something in the unit cell, aligned with the long axis of the cell,
with a periodicity corresponding to ~1/5 of the long axis. This can be seen
as greater intensities along the long axis every fifth spot. Without knowing
the unit cell parameters, I would guess it is either the interplanar
spacings of the nucleotides (probably this is too small) or the periodic
twist of the helix itself. Interesting that the RNA is a decamer ( = 2 x 5).
I would be curious to know what the unit cell parameters are, or more
generally, what is causing that noticeable periodicity...
Jacob
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Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: j-kell...@northwestern.edu
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----- Original Message -----
From: "James Holton" <jmhol...@lbl.gov>
To: <CCP4BB@JISCMAIL.AC.UK>
Sent: Wednesday, January 28, 2009 12:20 PM
Subject: Re: [ccp4bb] small lines in diffraction pattern
Hmm. I don't remember that thread. However, I personally think it is a
good idea to keep the "mosaic crystal" as Ewald and Darwin defined it.
Just because current integration software lumps things together into a
"mosaicity" does not mean that every mechanism contributing to the rocking
width of a spot should be given the same name. Especially when it is
difficult to describe the mosaic crystal using any other words. Perhaps
Colin could come up with a cool word for unit cell non-uniformity? Or is
he waiting for us to name it after him? "Nonuniform Anisotropic Variance
of Elasticity"? or "Cells Of Loose INdex"?
Comments and suggestions are welcome.
-James Holton
MAD Scientist
Jacob Keller wrote:
I had thought that in a previous thread, we had all come to a consensus
that actually the largest source of what is normally explained as
"mosaicity" is really differences in unit cell size, due perhaps to
uneven shrinkage in crystals upon freezing or otherwise. I believe that
there was actually an acta cryst paper which investigated all of the
various ingredients of "mosaicity" which supports this (this is why I
said it.)
Jacob
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: j-kell...@northwestern.edu <mailto:j-kell...@northwestern.edu>
*******************************************
