Dear all,

I used the command sel @N1 @N3 to select the N1 and N3 atoms of a nucleic acid structure (like 1bna).

when I do "show only" in Actions / Atoms&Bonds, a specific representation is displayed as in the image below: sticks connect N1 atoms of one strand and N3 atoms of the other strand.

May you tell me the meaning of this representation and how can I modify it (I mean, how to change the type of atoms to be connected)?

In fact, I would like to visually apprehend the helical axis. Is there a way to calculate and display this axis in Chimera?

Many thanks for your help

Damien