How certain are you of the space group? I ask because in all versions of PHASER that I have used to date, it chooses the space group (when SGALTERNATIVE is set) after placing the first molecule and with additional molecules it then assumes the space group result from the first molecule is the correct space group (the PHASER team is supposed to be rectifying this). While this is often the correct space group, I have seen several cases with both PHASER and other molecular replacement programs (e.g. AMoRe) where the correct space group only becomes evident after the placement of the second molecule. In particular, I have seen a case where after the first molecule was placed, one would have chosen P 21 21 2 on the basis of statistics provided, but after the second molecule was placed, it was clearly P 21 21 21.
Steven
