This representation applies much of the procedure used to construct the Tube. In the end, it connects the alpha-carbon atoms of successive residues by cylindrical segments with adjustable width. In the case of nucleic acids, it is the P backbone atoms which are connected. As always, the segment pieces are colored according to the atom they are associated with. If the cylinder radius is made 0.00, then the cylinder segments are replaced with lines.
Note: the Trace option is useful for people doing threading or protein
folding work who only look at the 
coordinates and residue
names, for then they don't have to build the sidechains necessary to
see their structure. Also, people working on polymers can fake their
structure by naming everything ``CA.'' in the PDB file and then using
Trace.