Rsr_zone [id two atoms] or [mol res1 res2]
The RSR_zone option is a flexible zone fitting option, allowing rotation/translation real space refinement of residue fragments to electron density. The user is asked to define a zone of residues by picking two atoms on the screen, or by specifying on the terminal, or (more likely) in a macro. A user definable fragment dictionary is consulted to decide how the individual residues are divided into fragments. The standard dictionary divides amino acids into a main chain fragment, and one or more sidechain fragments.
The RSR dictionary is maintained in the O database. There is an entry for each residue, with the name RSR_dict_xxx, where xxx is the three-letter code of the residue type. Each line in the entry corresponds to a fragment group. The dictionary can most easily be changed by editing a copy of the file $ODAT/rsr_dict.o. Alternatively, one can write out an entry on a local file, using
write rsr_dict_xxx junk.tmp ;
where xxx is the three-letter code of the desired amino acid. The entry can then be edited, and read into the database using
read junk.tmp
Since the name of the data block is part of the header, O knows where to put it.