Copyright information:Taken from "Crystallographic identification of an ordered C-terminal domain and a second nucleotide-binding site in RecA: new insights into allostery"Nucleic Acids Research 2006;34(8):2186-2195.Published online 28 Apr 2006PMCID:PMC1450331.© The Author 2006. Published by Oxford University Press. All rights reserved His99 and Asp122 belonging to an adjacent molecule in the filament.