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RE: [ccp4bb]: Non-merohedral twinning
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Either Bruker or Mar have some software that will index and process
multiple lattices -- most likely what I'm thinking of is GEMINI from
Bruker.
phx.
> -----Original Message-----
> From: Bart Hazes [mailto:bhazes@ualberta.ca]
> Sent: Wednesday, April 17, 2002 6:44 AM
> To: Roeland Boer
> Cc: ccp4bb@dl.ac.uk
> Subject: Re: [ccp4bb]: Non-merohedral twinning
>
>
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>
> On Wed, 17 Apr 2002, Roeland Boer wrote:
>
> > *** For details on how to be removed from this list visit the ***
> > *** CCP4 home page http://www.ccp4.ac.uk ***
> >
> > Hi there,
> >
> > I'm working on a dataset from a sample that is
> non-merohedrally twinned.
> > I got the twinning operation and can process the reflections of the
> > major component of the twin, but got a rather high Rint
> (11%). I thought
> > that the two lattices would not overlap too much, but
> apparently they
> > do. I'd like to detwin the data, and was wondering if
> somebody can point
> > out programs that can handle NON-merohedral twinned data.
> >
> > Thanks a lot,
> > Roeland.
>
> If this is a molecular replacement problem I'd just go on with MR and
> structure refinement. The Rint is indeed a bit high but the
> discrepancies
> between Fobs and Fcalc are dominated by imperfections in the
> model not the
> data and I think you can get a perfectly acceptable model if data
> completeness and resolution are ok. This is NOT an excuse for
> sloppy data
> collection and it will be fatal during experimental MAD/MIR
> phasing, but if
> you have the data already and can't easily get better data
> from a non-twinned
> crystal then you have my blessing.
>
> The alternative route would require that you can identify
> reflection overlaps
> between your twins. I don't know if there are programs
> available for general
> use to do this. Basically, I think you'll have to process the
> second lattice
> (in mosflm, just predict the spots from the first lattice and
> hand pick spots
> from the other lattice for indexing). The resulting MTZ files
> will have the
> spot position on the detector as well as the image number.
> You'll then have to
> write a small program, if none are available, to detect and
> reject reflections
> that overlap. If this is of general use I could consider
> adding such an option
> to SFTOOLS.
>
> Bart
>
> ==============================================================
> =================
>
> Dept. of Medical Microbiology & Immunology
> University of Alberta
> 1-15 Medical Sciences Building
> Edmonton, Alberta, T6G 2H7, Canada
> phone: 1-780-492-0042
> fax: 1-780-492-7521
>
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> =================
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>
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