In addition to Bert's statistics argument (I've never had the pleasure
of working w/ a C222 crystal), do check your self-Patterson map. I
recently had a difficult MR case; the crystal masqueraded as P21212 or
P2221, but it was actually P212121 with the two molecules in the AU
related by a non-crystallographic translation.
Dave Borhani
> -----Original Message-----
> From: CCP4 bulletin board [mailto:[log in to unmask]] On
> Behalf Of Roger Rowlett
> Sent: Friday, July 25, 2008 10:30 AM
> To: [log in to unmask]
> Subject: Re: [ccp4bb] MR problem --molrep
>
> Good point. One should always check all the screw axis
> combos. Not fun
> for P422, but Phaser makes this very easy, as it will do all the
> possible screw axis combinations in one job. The correct
> space group and
> MR solution is usually very obvious if the model is
> acceptable and the
> MR parameters have been set reasonably. I think Open-EPMR will also
> examine screw axis combinations now, but I've never used it
> to do this.
>
> Cheers,
>
> Roger Rowlett
>
>
> Phil Evans wrote:
> > Perhaps obvious - are you sure the space group is C222 not C2221?
> > Phil
> >
> > On 25 Jul 2008, at 14:19, Roger Rowlett wrote:
> >
> >
> >> Carl Soja wrote:
> >>
> >>> Dear all
> >>> I tried to solve one structure by ccp4i molrep(resolution
> at 3.0 A,
> >>> space group C222, sequence ID 30%). I can get a good Rfactor 0.528
> >>> at first translation function. However, the second translation
> >>> function Rfac is 0.526, the third is 0.525, the fourth is 0.525.
> >>> All of the translation function Rfacs are too closed. I changed
> >>> the model and minimum resolution for search, the Rfactor closed no
> >>> any improved. My structure estmates four molecules in the
> >>> aymmetric unit. This is my first time found the closed Rfac by
> >>> molrep. From the low translation function Rfac, it seems that it
> >>> is correct solution. I checked the solution and found some clashes
> >>> in the structure.I am not sure why the Rfactor too closed in next
> >>> the molecule search? I know this is unusual solution by molrep.
> >>> Does it mean the diffraction data has problem?
> >>> Any suggestions are welcome.Thank you in advance!
> >>> Carl soja
> >>>
> >> To be honest, I would try both Phaser and EPMR (now
> Open-EPMR) first
> >> to do MR. Both especially excel at finding good MR solutions for
> >> multimers, and are very fast as well. These programs can find
> >> solutions that are very difficult to find using other rotation-
> >> translation programs, including MOLREP. In my experience (using
> >> Phaser and EPMR) reasonable MR solutions almost always have an R-
> >> factor under 50%.
> >>
> >> Cheers,
> >>
> >>
> >> --
> >>
> --------------------------------------------------------------
> ----------
> >> Roger S. Rowlett
> >> Professor
> >> Colgate University Presidential Scholar
> >> Department of Chemistry
> >> Colgate University
> >> 13 Oak Drive
> >> Hamilton, NY 13346
> >>
> >> tel: (315)-228-7245
> >> ofc: (315)-228-7395
> >> fax: (315)-228-7935
> >> email: [log in to unmask]
> >>
>
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