Hi,
Do you have any biochemical evidence that points to oligomeric nature of your protein? Does SEC indicate monomer/dimer/trimer/tetramer?
If not or even if so, what does the crystal packing with your MR solution with 4 molecules suggest about monomer interactions? Does that correlate with SEC results?

Assuming your SG is correct, were you doing your MR search with a monomer? Does the packing with 4 molecules leave lots of space that can be potentially occupied by more monomers?

If so, and there is indication of dimer or trimer interactions, you could try your MR again and let's say search for 3 dimers or 2 trimers or 2 tetramers.

Also, what program are you using for MR and what is the resolution range for the Rot/Trans search?
If you are not using PHASER, you could try some different variations of resolution range for the search and see if you pick up more molecules.

What kind of refinement did you do after finding the 4 molecules? Have you tried simulated annealing refinement and then inspected the resulting maps at low sigma level to see evidence for additional molecules?
Also, how much sequence identity do you have between your target and search model? That can affect your map quality and R-factors quite a bit.

Regards,
Debanu.

Yanming Zhang wrote:

[log in to unmask]" type="cite">Sorry I forget to tell ya the details:

The SG of my Data is cubic P4332. Cell is 251.34A in all three dimensions.
Resolution is 3.1A. 5,6,7,8 might be the possible copies from Matthew
coeficient. But I just trust 6 because Chinese like the number 6
(happy Chinese new year by the way :)). No pseudo translation judged by Native Patterson. Self-rotation at the section kappa=180 shows strong peaks at phi=45 and psi=45.At the stage of map generation, the Rfree is 42% R is 38%.
Thanks!
Yanming

On Tue, 13 Feb 2007, Eleanor Dodson wrote:

Sometimes this sort of disorder is due to an error , so the first thing is to check very carefully that the solution makes sense.

Why are you so sure there are 6 copies in the asymmetric unit?

In situations like this I first worry about SG.

Is there a pseudo-translation vector? This can make it hard to decide on the SG..

Is there an alternate spacegroup with fewer molecules in the asymm unit?

What does the self rotation show?

Yanming Zhang wrote:

Dear All,

Maybe this is a trivial question:

My data should have 6 molecules in one assymetric unit. MR could find out 4 molecules. After this, no matter how hard I have tried, no more molecules can be found. At this stage, I suppose that all other copies are dis-ordered. And go ahead to do refinement with 4 molecules (ABCD) available.
The density for A is quite good. But for BCD are very dis-ordered. Many breaks in chains. I'd like to ask you:
In a situation like this, should I:
A, Use NCS for all copies?
B Do not use NCS at all?
C, Use NCS just for BCD? (even dis-ordered, but similar)?
What is the trick to lower down Rfree as soon as possible, if you have experienced the same situation before?

Thanks

Yanming