I have a 3.4 A (enzyme – protein only) map that I have fitted manually using 
Coot and automatically with Rapper. It all looks very nice – I can fit all but 
13 of the 330 residues. I have the following questions:

Does refmac5 have a way of refining the scale of the map? – I did my best to 
calibrate the microscope – but it would be nice to have the scale as a 
refinable parameter.

Is there a way of having Coot know that it is an electron map and not an x-ray 
map? The main issue is that carboxyls seem to be invisible and Coot tries to 
fit them as though the map had them there – which results in some pretty dopey 
stuff. The problem doesn’t seem to apply in refmac5 if you use the source EM as 
described in the instructions.

What is a reasonable starting weight for vdwrestraints ? Is there a rule of 
thumb for choosing this?

What are acceptable values for the Rfactor produced by Refmac5? The fit looks 
pretty good with an Rfactor of .39. What is the experience of the community in 
this regard?

Many thanks

Trevor Sewell


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