You pinpoint the most difficult part of the exercise; getting the
initial transformation.
If I had a rough model, I would do some refinement in the solved
crystal, then use that model as a search against the second form rather
than using electron density. The rotation and translation operators
will be what you need.
You can usually get the rotation very well from fitting one set of
experimental data against the other.
I use ALMN for that, see $CEXAM for a script - but Amore can do it as
well. (ALMN rotates the 2ns hklin to match the first so you need to put
Xtal2 as the first hklin and Xtal1 as the second hklin. You get all
pairs of symmetry operators listed, but one should be the same as your
rotation function for fitting the model against Crystal 2.
Once you have the operators, you can make a big mask in each form around
the models with a generous radius, and proceed using DMMULTI.
I must admit I always check the density generated under the mask, etc to
make sure it is in the right place!
Amore is my preferred MR search for this - it is flexible but prob.
phaser is too, once you get familiar with it..
Eleanor
Steven Muchmore wrote:
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All;
Could someone point me to a "how-to" on multi crystal
averaging using the CCP4 suite? I have a problem with
two crystal forms, and would like to see if I can both
improve the density and break model bias from a
molecular replacement sol'n in one of the forms.
Specifically:
How does one typically generate the initial mask to
cut
out the SF's for the search in to derive the RT
matrices between the forms? In my case, I have a
rough model in one of the two forms.
Does anyone have scripts for the entire process? I
have seen a couple floating around, but none that go
from mask generation to final inputs to dmmulti.
Thanks,
Steve
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