Re: aniso scaling

[Felix Vajdos <vajdos@gene.com>]

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Hello Annie,

I have seen this behavior too on many different structures and in many
different space groups, as have all of my colleagues.  I don't have a
good explanation for it, but my gut instinct tells me that it has to do
with the fact that Xplor scales Fobs, not Fcalc.  I can't really get my
brain around what may mathematically be happening, but our approach has
been to either 

1.  Set all atomic b-factors to an average value (I use the Wilson
B-factor if the data go out that far) before each round of anisotropic
refinement.  

2.  Subtract the average "increase" in B-factor from the atomic
b-factors before each round.  

I don't know about the validity of this approach, but it seems to keep
our b-factors in line.  I would be interested in what other people have
to say on the matter.

Felix Vajdos


-- 
*****************************************************************
Felix Vajdos                            ph.  650-225-6113
Postdoctoral Research Fellow            fax  650-225-3734
Department of Protein Engineering       e-mail vajdos@gene.com
Genentech, Inc.
1 DNA Way
South San Francisco, CA  94080
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