[ccp4bb]: Heavy Atom Negative Density

[Paul Hubbard <phubbard@post.its.mcw.edu>]

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Hello all,

I am having trouble trying to find out why I am getting negative density
for Fo(phic) maps calculated in SHARP. I managed to pull out possible Fe
sites from a residual map using the anomalous signal from the peak
wavelength (phases taken from data using just 1 Fe in the previous
round). The refined occupancies and B factors seem okay (~1.0 and 10.0),
and the FOM is okay (~0.35 to 3.0A for acentric reflections) - but the
denisty only looks good at -5 sigma.

This is from that 4Fe-4S MAD data I was having trouble with a few weeks
ago. Are these classic symptoms of some error I may have done? Any
suggestions gratefully appreciated.

Thanks

Paul

--
Paul Hubbard
Dept. of Biochemistry
Medical College of Wisconsin
Phone: 414-456 4305
Fax: 414-456 6510
URL: iris9.biochem.mcw.edu