I am asked to test ZANADU which is meant to sort out spacegroup anomalies!
Maybe your example can be the test case..
Eleanor
On Fri, 24 Mar 2023 at 14:21, Gianluca Cioci wrote:
> Hi Eleanor, Hi All,
>
> As suggested by Andrew (thanks!), I've switched off the NCS in Phaser and
> this gave a solut
Hi Eleanor, Hi All,
As suggested by Andrew (thanks!), I've switched off the NCS in Phaser
and this gave a solution in C2 (a=66.2 b=83.9 c=66.2 90 98.7 90)
that refines much better than the others (R=0.32/0.39).
Still, I am not 100% convinced this is the correct cell/spacegroup...
but it'
You have tried all spacegroups within point groups? P2 p21 c222 c2221?.
On Wed, 22 Mar 2023 at 03:01, Lijun Liu wrote:
> If data processing to be ok and all possible monoclinic and orthorombic SG
> gave unreasonable high Rs, maybe good to give a try with p1 space group?
> Since
> the p-lattice
If data processing to be ok and all possible monoclinic and orthorombic SG gave unreasonable high Rs, maybe good to give a try with p1 space group? Since the p-lattice indexing gave same a and b also very close alpha and beta, it could not exclude the possibility of p1 then twinned (also together
cell 66.3 66.3 83.9 90.2 90.1 98.7. P2 or P21 cell
Cell volume:364551.812
Data line--- cell 86.4 100.6 83.9 90.0 90.2 90.0. Cell volume double
- C2 or C222 or C2221 cell
Cell volume:729240.938. ie
How many residues in your model?
It is hard to decide much without
Hi Gianluca,
Have you checked for diffraction anisotropy problems? It might be worth
running it through the STARANISO webserver:
https://staraniso.globalphasing.org/cgi-bin/staraniso.cgi. Anisotropy can
make your data look twinned and elliptical truncation can help improve
maps.
Good luck!
Best,
Hello, can you give us a screenshot of a diffraction image, with the caveat
that they never look all that good with fine-slicing, still it might help ;-0
Also, an idea of the R-merge, R-meas, CC-half in some of those space groups.
Best wishes, Jon Cooper. jon.b.coo...@protonmail.com
Sent from P
Dear All,
I have collected a dataset from a small protein diffracting at 2.7A
resolution, here is the space-group determination from XDS:
* 44 aP 0.0 66.3 66.3 83.9 90.2 90.1 98.7
* 31 aP 1.2 66.3 66.3 83.9 89.8 90.1 81.3
* 14
Hi,
I have had twinning with P61, which makes it look like P6122. This is with
slightly asymmetric dimer.
You could try mol replacement in P65, and refine with twinning on. Maps should
look better if correct. Ben
Sent from my iPhone
> On 9 Jun 2021, at 10:13, Randy John Read wrote:
>
> I
I agree with Kay that, with a good model, solving in P1 is likely to be the
easiest comprehensive solution. If that doesn’t work, Phaser starts every
MR_AUTO job by making a list of all the subgroups, including the different
potential indexings (represented by Hall symbols), so you could also w
Hi Almudena,
if it is a packing problem, you need to find the correct subgroup of P6522
(179).
Take a look at
https://strucbio.biologie.uni-konstanz.de/xdswiki/index.php/Space_group_determination#Subgroup_and_supergroup_relations_of_these_space_groups
.
Subgroups of 179 are 20, 153, 154, 170, a
Maybe you have a bimolecular dimer when you expected a unimolecular
hairpin? It’s happened before :)
https://pubmed.ncbi.nlm.nih.gov/31584014/
Eric
On Tue, Jun 8, 2021 at 10:15 AM Almudena Ponce Salvatierra <
maps.fa...@gmail.com> wrote:
> Hello everyone,
>
> I am working with an RNA-only st
First spacegrouop - trigonal spacegroups can also be indexed as C2 so it
isnt so surprising that a P6/mmm should masquerade as C2.
I would look very carefull at the POINTLESS symmetry scores and see if some
are more convincing than others.
But how I hate RNA & DNA - molecular replacement struggle
It’s difficult to tell exactly what is happening from your description and the
attached image. Both your description and the image are OK. It’s just that
there are a lot of ways for things to go off the rails.
Are the molecules stacked end-to-end? In that case, you may have an
incommensurate st
Dear Petr
Both questions, on twin law and R-factors, are mainly questions about
definitions and standards.
From Online Dictionary of Crystallography: "The twin law is the SET of twin
operations mapping two individuals of a twin."
In your P 21 21 21 example with a=b, the set contains four oper
and I do not want to change
> the refinement program during the structure refinement.
>
you break my heart
:-)
> Thank you for your response,
> Petr
>
>
> From: Eleanor Dodson
> Sent: Tuesday, July 7, 2020 7:08:44 AM
> To: Pe
u for your response,
Petr
From: Eleanor Dodson
Sent: Tuesday, July 7, 2020 7:08:44 AM
To: Petr Kolenko
Cc: CCP4BB@jiscmail.ac.uk
Subject: Re: [ccp4bb] Twin law definition in REFMAC5
Is that twin law possible? Presumably the cell lengths for b and c are clos
Is that twin law possible? Presumably the cell lengths for b and c are
close but you are swapping a 2fold axis along c for a 21 axis along b?
Eleanor
On Tue, 7 Jul 2020 at 05:36, Petr Kolenko wrote:
> Dear colleagues,
> I have a crystal with space group P21212 and merohedral twinning according
>
Dear colleagues,
I have a crystal with space group P21212 and merohedral twinning according to
"-h, l, k" twin law. If I click "twin" in the interface, REFMAC5 recognizes a
different twin law and does not refine the structure properly. Is there a way
to tell REFMAC5 the proper twin law? I tried
: Thursday, April 21, 2016 3:08 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Twin and tNCS
Hi,
On your point 2, if this isn’t already a frequently asked question somewhere it
should be! With twinning, you have to decide first whether or not the crystal
appears to be twinned. This is done on the
Thanks all for your comments!
Yamei Yu
On Jul 5, 2014, at 5:10 AM, Nat Echols wrote:
> On Thu, Jul 3, 2014 at 7:50 AM, Nat Echols wrote:
> On Thu, Jul 3, 2014 at 6:53 AM, Dirk Kostrewa
> wrote:
> yes - unfortunately, in my hands, phenix.xtri
On Thu, Jul 3, 2014 at 7:50 AM, Nat Echols
wrote:
> On Thu, Jul 3, 2014 at 6:53 AM, Dirk Kostrewa
> wrote:
>
>> yes - unfortunately, in my hands, phenix.xtriage reads the XDS_ASCII.HKL
>> intensities as amplitudes, producing very different output statistics,
>> compared both to the XDS statistic
Sorry - the stats DO indicate perfect twinning - I misread the first Email..
Please ignore that comment!
Eleanor
On 4 July 2014 13:16, Philip Kiser wrote:
> Hi Eleanor,
>
> If I'm not mistaken, the mean I stats are indicating perfect twinning.
>
> Philip
>
>
> On Fri, Jul 4, 2014 at 4:49 AM
To answer the original question.
The indicators are that it is not twinned,
If the Mean s are close to the untwinned values - you can probably believe
it.
Why are you worried?
Eleanor
Determining possible twin laws.
0 merohedral twin operators found
0 pseudo-merohedral twin operators found
I
On Thu, Jul 3, 2014 at 6:53 AM, Dirk Kostrewa
wrote:
> yes - unfortunately, in my hands, phenix.xtriage reads the XDS_ASCII.HKL
> intensities as amplitudes, producing very different output statistics,
> compared both to the XDS statistics and to an mtz file with amplitudes
> created from that XDS
Hi Tim,
yes - unfortunately, in my hands, phenix.xtriage reads the XDS_ASCII.HKL
intensities as amplitudes, producing very different output statistics,
compared both to the XDS statistics and to an mtz file with amplitudes
created from that XDS file. I've contacted a phenix developer a few
we
Hi Dirk,
that would truely be very sad - the XDS file format is such a beautiful,
self-contained and well documented format for diffraction data that a
misinterpretation should really not happen.
Cheers,
Tim
On 07/03/2014 01:42 PM, Dirk Kostrewa wrote:
> ... and please check, whether phenix.xtri
... and please check, whether phenix.xtriage recognized the input data
as intensities or as amplitudes.
In case of doubt, convert the intensives first into an mtz file with Fs
instead of Is and run phenix.xtriage on the mtz file.
Best regards,
Dirk.
Am 03.07.2014 13:36, schrieb Tim Gruene:
H
Hi Yamei,
did you by any chance feed the output file from XDS into xtriage? It
would indicate the data were twinned even for a near perfect insulin
test crystal. After discussion with the developers I understand that
phenix does not seem to handle unmerged data well.
With phenix.xtriage V. phenix
Hi Yamei,
A possible explanation is that the actual space group is P4(2) but the data
are perfectly hemihedrally twinned, which makes the crystal appear to
possess 422 point group symmetry. No twin operators are found because
merohedral twinning is not possible in crystals with true 422 symmetry.
HI all,
I have a data set processed to P42 21 2 (the space group was suggested by
pointless ). then I use phenix.xtriage to analysis the data. I was confused by
the phenix.xtriage result.
According to the following number it is twin data, but why it couldn’t find any
possible twin law?
De
Dear Garib,
thanks for the clarification. I'll go back to the raw data and check for split
spots at high resolution (and give Mosflm a try; initially, the data were
integrated with XDS).
Cheers,
Uli
---
dr ulrich gohlke
Dear Uli,
It seems that you are dealing with psued-twinning when cell do not overlap
after rotation with twin operator. In these case what is in one resolution on
one of the orientation becomes another resolution in another orientation of
crystals
In short:. You have an operator R that relates
Dear colleagues,
I am in the process of refining a P2(1) structure that is marked by Scala as
twinned (L-test etc.) with a twinning fraction of ca. 0.2. I am still working
on the twinning problem, so no more details about this. But what puzzles me
right now is that, if I feed the data with a m
Hi Teresa,
As Eleanor has mentioned, you should probably check out other space
groups. Xtriage gives a lot of great information and many plots to
inspect. But, if you do not know what the plots mean and just look at
the results that say the twin fraction is 0.48 you can get into some
troub
If the twin law is k,h,-l, then your a axis must almost equal the b axis?
And if the twin fraction is 0.48 then you have additional symmetry I guess?
How sure are you that the point group is P4/mmm?
On 13 March 2014 20:41, Teresa Swanson wrote:
> Dear collegues,
>
> I'm working with a drug c
Dear collegues,
I'm working with a drug complexed protein structure that is having major
twinning issues. The drug has a single Br atom on a benzene ring, which I'd
like to use for orienting the drug in the binding site. I have various
anomalous data sets, ranging from 3.0A resolution, all sca
CP4BB@JISCMAIL.AC.UK
Onderwerp: [ccp4bb] twin refinement
Dear colleagues,
this is a request for comments on the evaluation of crystal structures that
resulted from twin refinement.
>From http://www.ysbl.york.ac.uk/~garib/refmac/Tutorials/refmac_tutorial.pdf:
"Although Rfactors are substantially
Dear colleagues,
this is a request for comments on the evaluation of crystal structures that
resulted from twin refinement.
>From http://www.ysbl.york.ac.uk/~garib/refmac/Tutorials/refmac_tutorial.pdf:
"Although Rfactors are substantially smaller with twin refinement than
without twin
refinement
The model is essentially 100% identical. The structure is of a point mutant
that has already been solved.
From: Tim Gruene [t...@shelx.uni-ac.gwdg.de]
Sent: Tuesday, July 30, 2013 5:26 AM
To: Jeffrey D Brodin
Cc: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb
of Tim Gruene
[t...@shelx.uni-ac.gwdg.de]
Sent: Tuesday, July 30, 2013 7:26 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Twin or underestimation of symmetry
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Dear Jeffrey,
how complete is you model, i.e. what is the ratio between the number
of
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
Dear Jeffrey,
how complete is you model, i.e. what is the ratio between the number
of atoms in the PDB file (without solvent/ ligands) and the expected
number of atoms as calculated from the sequence?
If a substantial part of the molecule is disorder
This is a bit puzzling.
Sticking to point groups:
P3 & P6 are sub groups of P6/mmm so data which merges in P6/mmm will
always satisfy P3 and P6.
And twinning in P3 or P6 will make the data seem to have higher symmetry.
Four way twinning is unusual, but possible of course.
But if you really have t
Hi everyone,
I have a dataset that's been giving me some trouble and wanted to get your
ideas on the best way to proceed. The data extend to ~2.6 Å and scale
integrate/scale well in P622. According to Pointless, the symmetry is either
P622 or P6322, however, neither Molrep norm Phaser finds mol
Is this twinning or several crystals indexed according to different
conventions? You usually see evidence of twinning for each crystal if it is
really there..
Trigonal data can be indexed as h,k,l k,h,-k -h,-k,l or -k,-h,-l of course
so you have a 75% chance of getting the 2nd crystal on a dif
Hi all,
Thanks for the express replies. Your insights along with the article by
Prof. Garib pointed to by Prof. Pavel completes the story for me.
Regards,
ARKO
On Fri, Mar 2, 2012 at 3:09 PM, Steiner, Roberto
wrote:
> On 2 Mar 2012, at 08:01, arka chakraborty wrote:
>
> Hi all,
>
> I will like
On 2 Mar 2012, at 08:01, arka chakraborty wrote:
Hi all,
I will like to know, as a follow up of what Prof. Randy Read said, what should
be done to do the refinement against the measured data and not the detwinned F(
which refmac outputs in the mtz after twin refinement), during subsequent
refi
1) You should use measured data (after scala/aimless/truncate). In general
there may not be one to one relationship between observed data and asymmetric
unit (e.g. non-merohedral twinning) and it would not be possible to bring input
data to output file. Use original data
2) Internally refmac gro
Garib may have more to say, but the first point would be to always include the
original data file as your input MTZ file for any cycle of refinement, whether
you're using Refmac in CCP4 or phenix.refine. (In phenix.refine, if you assign
the R-free data the first time you do refinement, it will
Hi all,
I will like to know, as a follow up of what Prof. Randy Read said, what
should be done to do the refinement against the measured data and not the
detwinned F( which refmac outputs in the mtz after twin refinement), during
subsequent refinements. And also, I would like to know how to ensure
I'm worried when you say that you use the initial job's output MTZ. Refmac
replaces F with a detwinned F in the output file so you wouldn't be refining
against your measured data in the subsequent round.
Best wishes
Randy Read
Randy J. Read
On 2 Mar 2012, at 02:00, wtempel wrote:
> De
Hi Wolfram,
a few points:
- R-factors in twin refinement vs non-twin refinement are not directly
comparable:
G.N. Murshudov, Appl. Comput. Math., V.10, N.2, 2011, pp.250-261
http://www.science.az/acm/V10,%20N2,%202011,%20pdf/250-261.pdf
- did you make sure free-R flags assigned "having twinnin
Dear CCp4ers,
A good morning to everyone.
Today, I have a structure that I initially refined in space group P6522,
1mol/asu.
Scaling stats (scalepack): 2.30-2.26A: Rsym=99.9%; / > 3
2.61-2.55A: Rsym=39.6%, / > 10
50.00-6.13: Rsym=6.4%
Some mild anisotropy in the resolution limits is apparent on the
.4261 | 0.4499 |
>-
>| << 4 | P 65 | 0.0596 |--| 0.1961 | 0.2315 |
>-
>
> R-factor in the ori
I see. Thank you for the reassuring and helpful pointers.
Best,
Peter
Subject: Re: [ccp4bb] Twin - Data reduction and refinement in Refmac
From: ga...@ysbl.york.ac.uk
Date: Wed, 13 Oct 2010 23:55:56 +0100
CC: CCP4BB@JISCMAIL.AC.UK
To: pc...@hotmail.com
It seems that evidence is convincing
have not used Bhat's omit maps before. I will give it a shot and see how it
may improve my model building.
Best,
Peter
> Date: Wed, 13 Oct 2010 17:35:09 +0200
> From: frederic.velli...@ibs.fr
> To: pc...@hotmail.com
> Subject: Re: [ccp4bb] Twin - Data reduction and refinement in R
e: Wed, 13 Oct 2010 21:51:57 +0100
From: ga...@ysbl.york.ac.uk
Subject: Re: [ccp4bb] Twin - Data reduction and refinement in Refmac
To: CCP4BB@JISCMAIL.AC.UK
As a general rule intensity based refinement gives higher R-factor especially
when intensities are weak. Truncate smoothes out data and Rfactors become low
As a general rule intensity based refinement gives higher R-factor especially
when intensities are weak. Truncate smoothes out data and Rfactors become lower
(it is not necessary that model becomes better)
In your case it may happen that your space group is higher. To check that you
can do simp
Hello All,
I am a graduate student working on my first merohedrally twinned data set. Like
a few, I am a bit intimidated by it. After some trial and error with the help
of some online resources and ccp4bb posts, I seem to have solved the structure.
However, I am still unsure about some of the
There isnt much evidence for twinning that I can see. Moments sensible,
Ltest sensible for untwinned data, some distortion of the cumulative
intensity plot but that could be due to integration problems.
Comparing Rfree in P3 is only proper if you have kept the same FreeR set
as you assigned in
On Thursday 08 July 2010 11:03:30 am Parthasarathy Sampathkumar wrote:
> Dear All,
>
> Back ground:
> This is my first experience with a twined dataset. Crystals belong to a
> small domain of 132 aa, out of which ~40 residues appears to be disordered
> (~30 of those from C-terminal and C-term His6
Hi Partha -
A few thoughts:
1. If you attach logs, at least gzip them ...
2. From the fact that Rfree goes down when twinning is switched off, I
would think there is no twining.
3. The intensity distribution (moment of E, etc) suggest no twining.
The twining operator you use is the crystallo
I guess you are using version 5.5. In that version in the beginning
the program finds all possible twin operators and assigns twin
fraction for each of them. Then it tries to filter out smaller twin
domains and takes only "significant" domains. I.e. when twin fractions
are higher than 0.05
Hi everybody,
can anybody tell me the difference between "twin domain" and "twin
fraction". Refmac just told me that my data have 12 twin domains
((pseudo)merohedral: one time: 0.113 and eleven times 0.081), but only 2
twin fractions ( 0.8924 and 0.1076).
best regards,
Paul
Hi,
You don't say whether you've considered the possibility that the true symmetry
is higher than P61, e.g. P6122. If there's higher symmetry consistent with
your data, then either pointless or xtriage will tell you which space groups to
consider for test refinements. Another good test (if yo
Hi
i am refining a protein strucutre with space group P61. Intesity statistics
doesnot suggest any twining but refmac and phenix xtriage suggest a twin
operator with fraction 0.48. when refined with this twin operator R factors
come dowm by 3-5% and also map looks much better. but upon closer ins
Dear All
this and other fixes are on the ccp4 problems pages
http://www.ccp4.ac.uk/problems.php
Charles Ballard
On 2 Mar 2009, at 16:50, Ronnie Berntsson wrote:
I have the same problem when running the latest ccp4 (6.1.1 on os
x, updated 1 hour ago via fink). Only way I managed to circumven
I have the same problem when running the latest ccp4 (6.1.1 on os x,
updated 1 hour ago via fink). Only way I managed to circumvent it is
to add the TWIN keyword in the command file as well..
Cheers,
Ronnie Berntsson
On Mar 2, 2009, at 16:06, Carr, SB (Stephen) wrote:
Dear CCP4BB,
I have
Dear CCP4BB,
I have come across a problem when running refmac5 in CCP4 6.1.1 via the
gui. I have a twinned data set and so want to refine the twin fraction
of the data. I selected amplitude based twin refinement in the gui, but
find that the resulting command file does not contain the twin keywo
Is it true that when doing twinned refinement REFMAC does not use the
assigned FreeR set?
Eleanor
Roberto Steiner wrote:
Hi Sabine,
If your question is: Is it possible to refine twinned structures with
Refmac?
My answer is: Yes. Very well.
Best wishes,
Roberto
On 20 Feb 2009, at 16:32
>
> I used phenix to assign the free reflections putting in the twin
> operators. Doing simulated annealing in phenix, I get a rather large
> difference in R/Rfree of ~7%. Well, I guess I need to do some tweaking of
> the parameters in phenix (running the latest phenix and cci_apps). When I
> tha
Hi Sabine,
If your question is: Is it possible to refine twinned structures with
Refmac?
My answer is: Yes. Very well.
Best wishes,
Roberto
On 20 Feb 2009, at 16:32, Sabine Schneider wrote:
Hi everyone,
I got good data to 2.4A on a protein-ligand complex. I want to
solve the
structure
Hi everyone,
I got good data to 2.4A on a protein-ligand complex. I want to solve the
structure by MR using a model with 45% seq. ID and 55% similarity.
Initially the data appeared to be P622 (pointless, selfrotation function
etc). Unit cell: 145 145 65, MW protein is 28kDa
I prepared the MR mo
L server.
http://www.ysbl.york.ac.uk/YSBLPrograms/index.jsp
Best wishes
Misha Isupov
From: CCP4 bulletin board [EMAIL PROTECTED] On Behalf Of Yuan, Hua [EMAIL
PROTECTED]
Sent: 26 November 2008 01:20
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] twin ax
I think you should be able to detect twinning from the intensity
statistics regardless of the spacegroup you have processed in...
Have you tried SFCHECK or looked at the truncate plots?
A word of warning - FreeRs and Rfactors for twinned data are somewhat
different to those for untwinned data,
Dear Colleagues,
I'd like to share with you with a twinning puzzle that's been
troubling me for a while.
I have a ~2.2 A data merged in p212121 space group with unit cell:
41.8300 117.4490 134.4840 90. 90. 90.
Translational NCS was detected but structure solution was able to b
Look at http://www.ccp4.ac.uk/dist/html/twinning.html for introduction..
Eleanor
Li Sheng wrote:
> Hi, Dear All,
>
> How could I know whether a crystal was twin or not from it's
> diffraction data?
> Thanx in advance.
>
>
>
>
> Sincerely,
> Li
> 07-08-2007
Hi, Dear All,
How could I determine whether a crystal was twin or not from its diffraction
data?
Is there any possibilities that a twin crystal contains P2 and C2 space group?
What's the characteristic in such a data file?
Thanx in advance.
Sincerely,
Li Sheng
2007-07-08
___
Hi, Dear All,
How could I know whether a crystal was twin or
not from it's diffraction data?
Thanx in advance.
Sincerely,
Li
07-08-2007
Here's an interesting paper on "The Genesis of Twinned Crystals" (from
1945! - it's even printed on simulated aged paper and if you look
closely the "aging" has an unrealistic plane-group pattern!):
http://www.minsocam.org/msa/collectors_corner/arc/twinorig.htm
It's by the eminent crystallograp
(lab)
-Original Message-
From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of
Christopher Colbert
Sent: Tuesday, April 17, 2007 4:01 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] twin fraction varies between crystals?
I experienced the same behavior. Crystals from the
:[EMAIL PROTECTED] On Behalf Of
Christopher Colbert
Sent: Tuesday, April 17, 2007 4:01 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] twin fraction varies between crystals?
I experienced the same behavior. Crystals from the same drop could have
varying twin fractions. Screening for twinning can
> -Original Message-
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Eleanor Dodson
> Sent: 18 April 2007 09:27
> To: Mark Mayer
> Cc: CCP4BB@jiscmail.ac.uk
> Subject: Re: [ccp4bb] twin fraction varies between crystals?
>
> This is a very common th
This is a very common thing - twinning is a sort of accidental overlap
of crystal fragments and thus will be different for diferent
"crystals". ( Should a twinned object be called a crystal? Discuss)
More serious - it is probably different for different parts of the data
collection if your cr
Hi Mark,
thus far, in the many cases where we had merohedral twinning, the twin
fraction varied usually a lot, ranging from ~0.1-0.5 for the same
crystallization conditions. So, it's a good idea to screen a couple of
crystals and check their twin fractions (estimating the true twin
fraction i
could anyone share their experience in seeding from a low-twin fraction
crystal found in a drop with high twin-fraction crystals?
-bryan
Mark,
I had a very similar problem. Varying twin fraction in identical drops -
no logical pattern. I eventually solved the structure as you seem to
have, screening dozens of crystals to find an untwinned crystal or at
least one with very low or statistically insignificant twin fraction
(which
I agree with you Mark. Even in my case the twinning fractions
varied substantially among the different crystals grown in same
drop. Moreover, I feel the fractions may vary at different part of
the crystal too. Please correct me if i am wrong.
regards
Manish
Mark Mayer <[EMAIL PROTECTED]> wro
I experienced the same behavior. Crystals from the same drop could have
varying twin fractions. Screening for twinning can be done with
remarkably few degrees of data. Of course, all proteins and all twins
aren't equal. So, don't expect to have varying twin fractions all the
time.
Happy R
Hi Mark,
Estimating twin fractions is best done on the basis of refining it with
a model. This can be done with phenix.refine or other programs like
shelx or CNS.
The ML estimate ofd the twin fraction relies on the correctness of the
sigmas. The 0.02 is actually the lower limit the ML proced
For cases where people have had merohedral twinning, did the twin fraction vary
substantially
between individual crystals grown under indentical conditions? I have no prior
experience with
merohedral twinning, and was surprised to see that the twin fraction varied
substantially as detailed
be
Dear All,
I have 1.4 A data and a molecular replacement solution for a crystal
indexed as C2, with beta approximately equal to 90. Refinement with
refmac is progressing poorly, and intensity statistics (Truncate) and
other twinning tests (xtriage) suggest pseudo-merohedral twinning with a
twin f
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