[ccp4bb]: Mosaicity-related questions......

[raji <raji@lamar.colostate.edu>]

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Hello,
Thanks to all the people who have given me input on my questions about high 
mosaicity and fine slicing. This is the 1st time I am handling these weird 
crystals. Jim's analysis estimates the crystal mosaicity to be ~ 0.3 (which is 
what I also got from Scalepack) while I thought the mosaicity was ~ 2.0 or 
more. 
My crystal has large unit cell dimensions and I was getting overlaps @ even 
0.2 deg. oscillations. Hence, I thought I could avoid overlaps by resorting to 
finer slicing. Now, in hindsight, I do not know if it was the best approach.
Here's some weird features of these crystals that have been a subject of 
discussion in our lab-
There are quite a few spots that appear to be due to twinning/splits. However, 
there are also several spots that are not predicted at mosaicity value 0.3.
If I find that I can predict more and more spots and maybe, predict most of 
the spots by increasing the mosaicity value in Denzo, what does that tell 
about my mosaicity? 
If the mosaicity is indeed 0.3 and if the xtal is twinned/split, then, where 
do  the spots NOT BEING PREDICTED at mosaicity of 0.3 come from? Are they from 
the 2nd lattice ? 
And, if the spots NOT BEING PREDICTED are from the 2nd lattice, then why does 
Denzo predict more and more spots when I increase the mosaicity value ? 
If Denzo is able to predict them at higher mosaicity, is it possible that 
those spots are from the same lattice ? 
How can I resolve unequivocally whether I have low or high mosaicity 
especially when my crystal seems to have some twinning/splitting ?
Thanks for your suggestions.
Ms. Raji

Rajeswari Edayathumangalam
Dept. of Biochemistry & Molecular Biology
Colorado State University
Fort Collins, CO 80523 USA