[phenixbb] SAD Phasing

Rajagopalan, Senapathy SRajagopalan at tmhs.org
Mon Apr 12 12:08:25 PDT 2010

Hi Everyone,

I have been trying to solve a structure of a protein-DNA complex using SAD data, but am running into problems and have some questions on how phenix solves it. From Mathews coefficient calculation, I know that my protein binds to the DNA as a dimer in the asymmetric unit. And when I use this information to specify the the number of heavy atoms to look for, I always get more (1.5-2X, depending on what resolution cutoff I use) in the final heavy atom sites pdb file. More importantly, the map looks 'incomplete' in the sense that part of one of the strands in the double stranded DNA is missing. My question is if this is the result of phenix using some incorrect sites (such as with low occupancy) while phasing. If so, then how can I fix it. I have tried deleting the low occupancy sites and reading the edited heavy atom sites file explicitly using sites_file=ha.pdb, but it doesn't seem to help.
Also, if I just use solve to find the heavy atom sites, those tend to be different too... Any suggestions here would be appreciated.


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