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SUMMARY:Using molecular replacement to exploit multiple crystal forms - pr
 ofessor Randy J. Read
DTSTART:20111019T091500Z
DTEND:20111019T101500Z
UID:TALK36344@talks.cam.ac.uk
CONTACT:23791
DESCRIPTION:One of the most powerful methods for phase improvement is to a
 verage multiple copies of density\, either from\ndifferent crystal forms o
 r from non-crystallographic symmetry within a single crystal form. \n\nTo 
 initiate averaging\, it is necessary to have both initial phases for all d
 ensity maps and the\nrotation/translation operators relating the various c
 opies of density.  Although it has been appreciated for\nsome time that mo
 lecular replacement can help achieve both of these requirements\, this app
 roach has not been\nadopted as widely as it should be.  We are aiming to m
 ake the tools much more convenient and\, if possible\,\nautomatic.\n\nMole
 cular replacement can be used in a variety of ways:\n\n· solve a second
  crystal form using copies of density cut out from the map of the first cr
 ystal form\n· define NCS operators within a single crystal form by find
 ing the operators that superimpose copies of\ndensity\n· superimpose a 
 poor model on density isolated from a single image in an experimental map\
 n\nOne surprising use of these tools is to find a recalcitrant copy in a d
 ifficult molecular replacement\nproblem.  Often it is possible to find som
 e\, but not all\, copies when using a poor model to solve the\nstructure o
 f a crystal with non-crystallographic symmetry.  It turns out that\, despi
 te model bias\, the\nmodel-phased density for a previously-placed copy pro
 vides a more sensitive model than the atomic model for\nfinding subsequent
  copies.\n\n
LOCATION:Seminar Room
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