Let's say I load 4 molecules, A, B, C, & D.  A and B are a heterodimer pair, as are C and D.  I'd like to move/rotate A and B together, maintaining their respective orientations, while holding C and D fixed (e.g., manually overlaying dimer structures). 
How do I do this?  I might have hit on the appropriate combination of protecting/freezing/creating objects/etc. once, but can't seem to repeat the routine. 
Thanks for any tips,
David Horita
David A. Horita, Ph.D.
Department of Biochemistry
Wake Forest University School of Medicine
Winston-Salem, NC 27157-1016
Tel: 336 713-4194
Fax: 336 716-7671
email:  dhorita@wfubmc.edu
web:  http://www.wfubmc.edu/biochem/faculty/Horita/