nab generated structure
 -- amber db.file -- 

DU
    0    0    0    0    0
  Strand   1: sense
D   0    0    1    3    0
DG  2DC  2DG  2DT  2DT  2DA  2DA  2DC  2DG  2DC  2

  Strand   2: anti
D   0    0    1    3    0
DG  2DC  2DG  2DT  2DT  2DA  2DA  2DC  2DG  2DC  2

QUIT