Hi Fred,

it's a shame these data were not submitted to the PDB - the cif-file for 4JMQ 
only contains the P1 data, although the cif-format supports several data sets 
in one file. Did you attempt submitting the anomalous data to the PDB at that 
time?

Best,
Tim


On Monday, April 04, 2016 08:28:30 AM Vellieux Frédéric wrote:
> Hi,
> 
> I think this “look for another crystal”  is indeed a bit too negative. For
> example, Flayhan et al. [(2014), J. Virol. 88, 1162-1174] managed to solve
> the structure of bacteriophage T5 pb9 by Europium SAD using a twinned
> crystal (twinnjing fraction = 0.3), with an initial figure of merit of
> 0.15. So such data are not hopeless in fact, giving up was certainly not
> the thing to do in that case.
 
> Fred.
> 
> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
> Eleanor Dodson
 Sent: Saturday, April 2, 2016 6:06 PM
> To: [log in to unmask]
> Subject: Re: [ccp4bb] SAD/MAD with Twinning
> 
> hmmm - in the ideal world with perfect data and a twin factor < 0.5 you
> would detwin your data before trying sad or mad..
 
> But detaining inevitably increases the Sigmas so a weak signal can be
> lost..
 The lab philosophy was - if you need to do expel phasing, and the
> data are twinned look for another crystal … But that may be too negative. 
> You could try it and see if the phasing improved.
> 
> Eleanor
> 
> On 1 April 2016 at 21:40, Keller, Jacob
> <[log in to unmask]<mailto:[log in to unmask]>> wrote:
 Dear
> Crystallographers,
> 
> It occurred to me that SAD/MAD would work much better by incorporating
> twinning into the HA finding/refining/phasing stage, since the Bijvoet
> differences could be split according to the twinning fraction and/or the
> HA's would be transformed by the twin operator and weighted by alpha and
> (1-alpha). I believe twinning is not currently modeled during this stage,
> even though for twinned structures this would dramatically improve things
> almost to the level of untwinned data, I think. Twin fractions could be
> determined at the HA stage, then everything would go more smoothly. Any
> thoughts of such an implementation? Perhaps Shelx does this since 1969 or
> something?
 
> I thought of this because I saw some really deep "holes" in the Phaser
> output from a twinned dataset, and think these might be the evil other twin
> sneaking in?
 
> JPK
> 
> 
> *******************************************
> Jacob Pearson Keller, PhD
> Looger Lab/HHMI Janelia Research Campus
> 19700 Helix Dr, Ashburn, VA 20147
> email: [log in to unmask]<mailto:[log in to unmask]>
> *******************************************
> 
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Paul Scherrer Institut
Dr. Tim Gruene
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