DNA

DNA is an expert system which takes test images of your crystal of interest, autoindexes the images and makes a strategy prediction based on the laue class and uses BEST to suggest exposure time to be used. It can then collect your data and integrate the resulting data set using MOSFLM.

DNA be run through a stand alone gui using this icon  found on the right hand screen on each beamline computer.  Several videos showing you how to use DNA can be found here.

There is also a tab within MXcuBE this uses the DNA server, which can be started using this icon.

Currently installed version

The following version is installed on all ESRF beamlines (ID14-1,2,3,4, ID23-1,2 and ID29) and as well on the CRG BM14:

DNA version 1.1 November 17th 2008

Manual:

This manual was written by a collaboration of the EU-BIOXHIT-TID centres in Oulu and Crete and the program developers of DNA at the ESRF.

Known issues:

• The resolution estimation can be wrong in some cases. Therefore always check the resolution proposed by DNA by examining the images manually.
• The exposure time estimated by BEST has also been reported to in some cases not be realistic. It is therefore necessary to control also this value.
• DNA sometimes gets stuck due to server problems - this needs a DNA expert to fix but if there is no one on site you can run DNA in safemode.

  DNA strategy is only calculated to the edge of the detector. If the ‘best resolution’, which is determined by an extrapolation, is higher than this resolution at the edge of the detector then you need to move the detector and collect new reference images to higher resolution and rerun DNA.

1. Why does DNA always use very small phi angles ?  DNA calculates a data collection strategy to optimize the highest resolution with a specified completeness and multiplicity (both of which are specified in the gui).  To optimize resolution it suggests a strategy which maximizes signal to noise in the highest resolution shell and this often needs fine phi slicing which can take time to collection.  If you are limited by data collection time you need to specify a Minimum phi osc – to restrict fine phi slicing. Warning – using large oscillation angles may result in overlaps in your data !!

2. What is Tmax ? Currently we 'guess' how long a crystal will survive in the beam, this maximum time in the beam or Tmax is specified in DNA.  This estimation assumes that the beam transmission is 100% and that the crystal is the same size or smaller than the beam size. If the beam is attenuated or the crystal is significantly larger than the beam then longer data collection times can be used.

3.  DNA error – total exposure time exceeds limit - what should I do ?  The strategy suggested by DNA has a total exposure time greater than Tmax, if you want to go ahead and use this strategy click ‘ignore max exposure time’ and continue.

4. Should I believe the DNA strategy ? Yes, unless your crystal is much bigger than the beam.  DNA assumes that the crystal is the same size or smaller than the beam and determines a strategy accordingly.  If your crystal is larger than the beam size or you are using helical data collection you can accept significantly longer exposure times. DNA assumes 100% transmission so if you have attenuated the beam you can modify the DNA strategy accordingly.

5. Why does DNA indexing fail ?  DNA has been set up so that automatic integration can follow a successful indexing – therefore the criteria for accepting a good indexing solution is rather strict – this is a beamline setup and can not be changed.  If DNA indexing fails because of a high rms values you need to run another strategy program.