A short DNA double helix composed of palindromic DNA represented as a molecular surface.

http://en.wikipedia.org/wiki/Palindromic_sequence

The Coordinates come from the Protein Data Bank entry 1SK5:

http://www.rcsb.org/pdb/explore.do?structureId=1sk5

The DNA sequence is:
5'-CTTTTAAAAG-3'

STL file created using VMD:

http://www.ks.uiuc.edu/Research/vmd/

Models successfully printed in PLA on a Makerbot Replicator 2 using MakerWare 2.2.2.89, standard resolution with raft and supports, 15% infill, 2 shells. Each model represents a single DNA strand. The two models should fit together snugly without excessive force.