I just wanted to check that you're using an up-to-date version of Phaser, which will account for the presence of translational NCS (tNCS).  With older versions of Phaser, you could get apparent solutions that were incorrect but would give a high LLG just because they satisfied the tNCS.  However, even with the current version of Phaser there's a potential problem here.  Phaser will only take account of the tNCS if you're looking for an even number of copies (so that it can look for pairs related by the tNCS).  I'm wondering if, in your case, the tNCS is generated in the model by placing the heterotetramer with its internal 2-fold parallel to the 2(1) screw axis along y.  If that's the case, and you're only looking for one copy of the heterotetramer, then I'm afraid Phaser will ignore the tNCS.  If indeed you're only looking for one copy of the heterotetramer, could you try looking for two copies of the half-tetramer instead (in the new version of Phaser)?  That may give a clearer indication of the true symmetry and, if the solution is correct, the combination of translational symmetry and the screw axis should generate a full tetramer.

 

In cases like this, there's always a potential issue with twinning.  I'd be interested in seeing the logfile (off-list) for the Phaser run, which should give an indication of whether the intensity moments suggest twinning, once the statistical effect of tNCS has been accounted for.

 

Best wishes,

 

Randy Read