If the user chooes the F option, the resodues is built in the forward direction in the sequence, with B ackwards, with C at the current screen centre. This generates coordinates for a possible rotamer. In the above example, the residue is an alanaine and does not have a rotamer. The dictionary is a text datablock, and therefore can be read in at start-up or with the Read command. It contains free format text, with a keyword at the beginning of a line.
Lines starting with an unknown keyword are simply skipped.
Some keywords are only relevant to some commands, e.g. the 'centre' keyword is only used by the Template building system only, while the 'rotamer' keywords are only used by the roatmer commands. It is therefore important that the number of lines in the header should match with the contents. This residue has 3 rotamers, and only one angle takes on different values. The amino-acid rotamers in this file are the result of an analysis made by Gerard Kleywegt. The names provide an idea of their frequency.