Swapna replaces every residue with at least one atom in atom-spec with a new_type residue. New_type is a one-letter code representing one of the standard nucleic acid bases: A, T, G, C, or U. New_type can be in lowercase or capitalized. Residues swapped into models with hydrogens will include hydrogens, whereas residues swapped into models without hydrogens will not. (Note that hydrogens can be added with AddH.) The geometries of the new residues may not be optimal.
The temperature factor for the new residue is set to the highest currently found in the model.