Bone_Ca_zone [Id 2 atoms] [molecule] [start residue] [direction]
This command is intended to help in the construction of CA traces. It would normally be used after using the Bone_prune command to create something that looks like a trace. All atoms between the identified atoms are taken to be CA atoms of the molecule being constructed. The identified atoms cannot be joined in a circular connection. It is only necessary to specify the start residue of the molecule under construction. The direction can be forwards or backwards in the chain. If an object CA has been constructed, it will be redrawn.