To show further how one might handle oligomeric proteins I have a larger example of structure definition. It is taken from the Cro structure. Cro crystallizes as a tetramer of chemically identical monomers related to each other by non-crystallographic symmetry. First the CHAIN statements are given. They are very simple because there are no interchain links and all the monomers are of the same type. Next I have given the first few RESIDUE statements defining the amino acid sequence of the chain type CRO. The sequence need only be given once because even though there are four chains (O, A, B, and C) there is only one chain type (CRO).
CHAIN O CRO CHAIN A CRO CHAIN B CRO CHAIN C CRO RESIDUE CRO|1 MET 2 PEPT RESIDUE CRO|2 GLU 3 PEPT RESIDUE CRO|3 GLN 4 PEPT RESIDUE CRO|4 ARG 5 PEPT RESIDUE CRO|5 ILE 6 PEPT ATOMC N -23.5711 -21.5563 -17.6677 47.89 1.00 N 1 O ATOMC C -24.9299 -22.0883 -17.5977 28.88 1.00 CA 1 O ATOMC N -31.6302 -17.6350 -27.8797 28.57 1.00 N 1 A ATOMC C -31.4544 -19.0311 -27.6180 29.61 1.00 CA 1 A ATOMC N -28.8195 -34.1503 -19.6577 44.24 1.00 N 1 B ATOMC C -28.6735 -32.8969 -20.4065 59.62 1.00 CA 1 B ATOMC N -39.9969 -26.5889 -24.4465 44.30 1.00 N 1 C ATOMC C -38.9848 -25.8469 -23.6391 34.11 1.00 CA 1 C