Thanks. Your suggestion remind me that I forgot to mention one more
information. Actually, I did try to shot different regions of crystal
to reduce radiation damage. Say, the sca1 set used one region and the
sca2 set used another. Is it possible that this two regions has
different crystal domain arrangement (one is normal and another is
twinned)? The crystal looks like a nice single crystal.

Zhiyi

On 1/5/12, Carlos Frazao <[log in to unmask]> wrote:
> Hi
>
> If the beam cross section is significantly smaller then the crystal
> dimensions, when you rotate the crystal you will be constantly
> illuminating new volumes of the crystal. If the crystal contains
> differently oriented "single crystal domains" (that is indeed a twinned
> crystal) then you may have orientations where only one of those "single
> crystal domains" are being measured, and other orientations where
> multiple "single crystal domains" are collected. The same applies if you
> apply translations at the crystal (to collect data from  fresh crystal
> regions to decrease the radiation damage effect).
>
> Hope it helps, cheers,
>
> Carlos
>
>
> Zhiyi Wei wrote:
>
>>Thank you for all the quick reply. Here are the additional information
>>about the crystal. The crystal was frozen and shot in synchrotron. The
>>collection was 1degree/frame. The space group and unit cell are P21
>>and  a=70 b=165 c=170 alpha=90 beta=90.1 gamma=90. I processed the
>>data in P1 first (I did not see any abnormal changes during
>>integration), and then merge them using P21 or P2221. P21 gives
>>reasonable Rmerge of ~10% while P2221 has much higher Rmerge of ~30%.
>>I reprocessed the data with mosflm using P1. And Pointless also
>>suggested the space group of P21.
>>
>>Zhiyi
>>
>>On 1/5/12, Jens Kaiser <[log in to unmask]> wrote:
>>
>>
>>>What are your cell constants and space group? It sounds to me you
>>>misindexed and then artificially "twinned" your structure by
>>>integrating/merging in too high of a symmetry. I've seen that happen for
>>>primitive hexagonal which was actually C-centered monoclinic.
>>>Also, in my experience this is more likely to happen with
>>>denzo/scalepack as it refines every image and does postrefinement in
>>>scalepack. XDS will decide for you on a symmetry after integration, and
>>>in MOSFLM you should see earlier that something is wrong.
>>>
>>>HTH
>>>
>>>Jens
>>>
>>>
>>>On Wed, 2012-01-04 at 21:42 +0800, Zhiyi Wei wrote:
>>>
>>>
>>>>Dear all,
>>>>
>>>>I recently collected a dataset (~2000 frames) from a single crystal.
>>>>If merge first 600 frames (sca1) or last 600 frames (sca2), Rmerge
>>>>values from scalepack seem to be ok (~10%) though rejection ratios are
>>>>high (~5%). But if I merge all frames together, Rmerge value goes up
>>>>to ~20% and rejection is extremely high (~20%). Then, I checked sca1
>>>>and sca2 by xtriage in phenix. Surprisingly, the logfiles told me that
>>>>sca1 is no twining while sca2 is very likely to be twinned. I never
>>>>met this case before. So, I am wondering if it is possible from a
>>>>non-twinned structure to a twinned structure just due to radiation
>>>>damage. If the answer is yes, does it mean that I should not collect a
>>>>large number of frames to amplify anomalous signals by using this
>>>>crystal?
>>>>
>>>>Thanks a lot!
>>>>
>>>>Best,
>>>>Zhiyi
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>
> --
> **************************************
> Dr. Carlos Frazao
> Structural Biology Laboratory -
> Macromolecular Crystallography Unit
> ITQB-UNL, Av Republica, Apartado 127
> 2781-901 Oeiras, Portugal
>
> Phone:  (351)-214469666
> FAX:    (351)-214433644
> e-mail: [log in to unmask]
>         www.itqb.unl.pt
>
>