(a) Experimental scattering curve of the RecN head domain. The pair distribution function [P(r)] is shown in the inset. (b) Model built by DAMMIN. Several independent models were averaged and filtered in order to obtain the most probable envelope. Length and width are indicated. (c) Superposition of the crystal structure of the pfRad50 ATPase domain with the ab initio model obtained for the RecN head domain in solution.