That’s a reasonable explanation. Another possibility is that there really isn’t room in the asymmetric unit of your cubic unit cell for a 7kDa protein. That could either be because you’ve inadvertently crystallised something else, or because the true symmetry is lower (and therefore the asymmetric unit is larger). The apparent symmetry could be higher than the true symmetry if you have a twinned crystal. What do the twinning tests say (particularly the intensity moment tests)? Best wishes, Randy Read On 30 Apr 2014, at 00:17, Nathaniel Echols wrote:

On Tue, Apr 29, 2014 at 5:34 PM, Subhani Bandara wrote: I am trying to solve the structure of 7 KDa protein with a cubic space group at 1.35A resolution with Phaser-MR. It gives the error massage saying "The composition you have entered has a protein/nucleic acid content of 300.3%, which is impossible. Decrease your composition" and stops. This appears even if I give one chain as search model and say there is only one component copy. How can I fix this.

The most likely explanation is that your sequence file contains multiple copies - or perhaps it contains the entire sequence of a large protein and you're working with a single domain?

-Nat _______________________________________________ phenixbb mailing list [email protected] http://phenix-online.org/mailman/listinfo/phenixbb

------ Randy J. Read Department of Haematology, University of Cambridge Cambridge Institute for Medical Research Tel: + 44 1223 336500 Wellcome Trust/MRC Building Fax: + 44 1223 336827 Hills Road E-mail: [email protected] Cambridge CB2 0XY, U.K. www-structmed.cimr.cam.ac.uk