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
*******************************************
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: [log in to unmask]
*******************************************
----- Original Message -----
From: "James Holton" <[log in to unmask]>
To: <[log in to unmask]>
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: [log in to unmask] <mailto:[log in to unmask]>
>> *******************************************
>
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