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Re: [ccp4bb] unbiased electron density map |
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CCP4bb navigationCCP4bb <-- 2008 <-- January 2008 <-- 10 January 2008Subject: Re: unbiased electron density map From: Dale Tronrud det102 {- at -} UOXRAY {- dot -} UOREGON {- dot -} EDU Date: 2008-01-10 > > Am 10.01.2008 um 01:53 schrieb Dale Tronrud: > ... >> Your quote bring up another matter. An "initial" map, i.e. before >> refinement, is unbiased if it is an omit map. If you have done no >> refinement and you leave the interesting part out of the calculation >> of Fc there can not be any bias in either the Fo-Fc or the 2Fo-Fc map. >> This is why an initial map is more reliable for proving binding of >> a compound, for example, than a bias reduced map after refinement. > ... > > But isn't this only true, if the model that is put in was not refined > against a related data set before? If the new Fobs are related to the > old Fobs (against which the model was refined before) then you carry any > model bias over to the new data, because a simple omit-map using the old > data will have model bias. > Right you are, and it's an important point too. My only defense is that I said "If you have done no refinement...". I don't think of the refinement of several models to data from isomorphous crystals as separate refinements, but sometimes forget to mention this when talking to others. I should be more careful. Dale Tronrud CCP4bb navigationCCP4bb <-- 2008 <-- January 2008 <-- 10 January 2008 |
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