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On Tue, 29 Aug 2006, zzj wrote:
> Hellow everyone,
> I am doing MR in phaser. My spacegroup is p63. I expect 4 molecules in ASU.
> The MR_FRF peaks seem not bad:
> SOLU TRIAL ENSEMBLE hgl EULER 18.943 154.679 344.874 ZSCORE 4.51
...
> However, when I perform MR_FTF, translation along Z is zero:
> SPAC P 63
> SOLU SET RFZ=4.0 TFZ=4.7
> SOLU 6DIM ENSE hgl EULER 42.074 104.646 182.842 FRAC 0.18098
> 0.27601 0.00000
> SOLU SET RFZ=3.6 TFZ=4.6
> SOLU 6DIM ENSE hgl EULER 28.819 24.287 68.541 FRAC 0.03388
> 0.76660 0.00000
...
> When use MR_AUTO, there's no such problem although it didn't seem to
> find any correct solution (according to Zscore and LLG).
> Is this the problem of phaser or just the statistics has been messed
> up by some translational NCS? How can I check this?
> Any advice is very appreciated.
> JOE
If I remember correctly, in these space groups (like in P2(1) for example,
with the 2(1) axis) the origin is not defined along the 6 fold axis, z.
Hence looking for just one molecule should use an arbitrary value of z,
apparently z=0.0 is chosen by the program. I personally prefer z = 0.12345
as an arbitrary value but that's a question of taste.
Placing a fist molecule defines the origin along z. Afterwards, placing a
second molecule implies that a search should be made along z and so
forth for the third molecule...
MR_AUTO will do this automatically, place a first molecule then perform
the correct translational search (including z for 'later' molecules),
so it is the method of choice for such a space group. Just easier.
I haven't peeped enough into the Phaser manual to know how to perform the
correct search along z if the program is used in 'manual mode',
i.e. performing an additional search along z once the four molecules have
had their positions along x and y determined individually. I'm sure it's
possible but I don't know how... Perhaps Randy will let us know.
Fred.
--
s-mail: F.M.D. Vellieux (B.Sc., Ph.D.)
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