Table 3.

Structural comparison of the main chains of the RNase A monomer, the RNase A dimer, and the BS-RNase dimer, giving the root-mean-square deviation (rmsd, in Å) of the functional units (FU)^*

	RNase A-FU†	RNase A-FU1	RNase A-FU2	BS-RNase-FU1	BS-RNase-FU2
RNase A-FU	0	1.3	1.3	1.1	0.6
RNase A-FU1		0	0.5	1.4	1.2
RNase A-FU2			0	1.5	1.3
BS-RNase-FU1				0	0.9
BS-RNase-FU2					0

^*The functional unit in RNase A is the monomer without the hinge loop (residues 16–22), and in the dimers is the monomer-like unit made up of residues 1–15 and 23–124 but lacking the hinge loop. Notice that all of the functional units have essentially the same structure. The functional unit is essentially the same in all three structures; only the hinge loop is changed, which results in a very different dimeric structure. 

^†The definition of functional units are as follows. RNase A-FU: RNase A monomer functional unit, residues 1–15 + 23–124; RNase A-FU1: RNase A dimer functional unit 1, residues 1–15 + 223–324; RNase A-FU2: RNase A dimer functional unit 2, residues 201–215 + 23–124; BS-RNase-FU1: BS-RNase functional unit 1, residues 1A–15A + 23B–124B; BS-RNase-FU2: BS-RNase functional unit 2, residues 1B–15B + 23A–124A.