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RE: [ccp4bb]: Problems with low mosaicity



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I suspect the problem is not with loop vibration.  The mosaicity is
primarily going to be a function of the incident beam in this case.  

A similar experience occurred recently with us collecting very high
resolution data with a short wavelength.  Initially the data looked awful
even thought the mosaicity was 0.17 degrees and the spots extended of the
edge of the image plate.  The Rsyms were high and many bad reflections were
seen on the xdisp display. 

The reflections were close together so we immediately checked the beam
center in case the crystal had been misindexed.  The beam center was fine
but in greping the .x files we found that the unit cell was running away
with us over successive images.

On the advice of staff from SSRL (cheers Ashley/Jessica) we reduced and
decoupled some of the refinement parameters for the denzo integration and
over a sleepless night produced a 5.5% final R, 0.95A, 2sigma highest
resolution shell for a ~170kDa system.  What appeared to be quite bad data
was in fact very good - the maps look beautiful.  The main problem seemed to
be over fitting and the reflection separation, which was small given the
resolution, cell and wavelength.  

I've suggested this to the author but I'll repeat it here.  It's worth
looking at the .x files to check that parameters are not running away then
check what is being fitted.  Once again thanks to SSRL for their help.

Cheers,

Eddie

Edward H. Snell. Ph.D.	
Email:eddie.snell@msfc.nasa.gov

NASA Laboratory for Structural Biology
Code SD46, NASA MSFC 	  Fax:	256 544 9305
Huntsville AL 35812, USA  Phone:  256 544 5570
Telepathy: 42.2 GHz       Mobile:  256 653 8677
Heisenberg was probably here!



-----Original Message-----
From: Jeroen Mesters [mailto:jmesters@imb-jena.de]
Sent: Wednesday, March 06, 2002 10:06 AM
To: ccp4bb@dl.ac.uk
Subject: Re: [ccp4bb]: Problems with low mosaicity


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***          CCP4 home page http://www.ccp4.ac.uk         ***

Hi,

I don't quite understand how vibration and low mosaicity fit together.
Vibration should increase mosaicity and smearing of your spots!

Certainly trivial to say, are You sure you have the center of beam
correct!?!
We have had a similar case, nice images but the Rsym...

Jeroen.
-- 
Jeroen Raymundus Mesters, Ph.D.                           Alias Geronimo
Dept. of Structural Biology and Crystallography,  Institute of Molecular
Biotechnology, P.O.Box 100 813, D-07708 Jena, Germany.
Tel: +49-3641-656063, Fax: +49-3641-656062, E-mail: jmesters@imb-jena.de
http://www.imb-jena.de/www_sbx/home.html
--
If you can look into the seeds of time and say
which grain will grow and which will not - speak then to me    (Macbeth) 
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