Summary: The general procedures are: First, a rigid body global search is performed and geometrically plausible protein–nucleic acid complex structures are generated. In this process, user-defined restraints can be applied to limit the search space. The resulting models are scored and ranked using statistical potentials, developed specifically for protein–RNA or protein–DNA complexes. The best-scored structures are then clustered and representatives of the largest clusters are selected for structural optimization by energy minimization before being presented to the customer.