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:[EMAIL PROTECTED] On > Behalf Of Roger Rowlett > Sent: Friday, July 25, 2008 10:30 AM > To: [email protected] > 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: [EMAIL PROTECTED] > >> >
