Dear all,
I would like to share my experiencde with a rather unexpected problem
of indexing conventions. Perhaps I can save people some time....
I have a crystal in the more unusual P21212 space-group (No 18). Its
unit cell lengths are b>a>c (please note). I systematically use XDS
for data integration, since so far it was able to handle even the most
horrible-looking spots.
Now XDS indexed my data in space-group 18, but with the axes order
a<b<c! It had, in fact, "invented" a space-group P22121, which does
not exist. I did not realise this until I had spent a couple of weeks
with beautiful peaks in rotation functions, but hopeless results in
translation functions. It wasn't until I looked more closely into the
definition of the screw axes that I realised the problem.
POINTLESS does not allow a reindexing of reflexions within the same
space-group, but fortunately REINDEX did the trick at the level of
intensities, because I like to use SCALA for careful scaling of my data.
So, basically, beyond just warning people who might encounter similar
problems, I was wo,dering if XDS could perhaps reindex reflexions
according to Int. Table conventions once the screw axes of a crystal
system have been identified?
With best wishes,
Anita
Anita Lewit-Bentley
Unité d'Immunologie Structurale
CNRS URA 2185
Département de Biologie Structurale & Chimie
Institut Pasteur
25 rue du Dr. Roux
75724 Paris cedex 15
FRANCE
Tel: 33- (0)1 45 68 88 95
FAX: 33-(0)1 40 61 30 74
email: ale...@pasteur.fr
