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] >>