Compound active center in dimeric ribonuclease III (RNase III) suggests a mechanism for double-stranded RNA (dsRNA) cleavage (Blaszczyk J, Tropea JE, Bubunenko M, Routzahn KM, Waugh DS, Court DL, and Ji X. Structure 2001; 9:1225-1236. Abstract). Left: Ribbon diagram of molecules A (green) and B (blue) illustrates the formation of a compound active center at each end of the dimer interface with residues from both subunits. Right: Surface representation (red and blue indicate negative and positive potentials, respectively) of dimeric RNase III endonuclease domain highlights the valley at the dimer interface, which can accommodate a dsRNA substrate.