1>-:...2_:[.DA]A-----T[.DT]:..11_:-<...1
This is an
ad hoc format specifying the two nucleotides in a pair. Starting from the left,
1>-:...2_:[.DA]A, here
1 means model number,
2 is the residue sequence number, and
DA is the residue name, and
A is the one-letter abbreviation. So here it means A (named DA for DNA) with sequence number of 2, in model number 1. The same idea applies to the right hand side, just with order reversed. Please see
http://www.wwpdb.org/documentation/file-format-content/format33/sect9.html for a description of the Coordinate Section of the PDB format.
I know this cryptic format is not intuitive, and not well documented. However, it has been there for so long, and it will stay with the 3DNA v2.x releases. If you have tried DSSR, the residue identifier is much more flexible, and well documented (the
--idstr option, see the "
DSSR User Manual").
HTH,
Xiang-Jun