Symmetric Fitting DNAb Helicase

Shows how to fit a molecular model into an electron microscopy map taking into account clashes between symmetrically placed molecules. Example is DNAb helicase, a hexameric ring which splits double stranded DNA during DNA replication in bacteria (EMDB 1022) fit with 3 copies of a crystal structure of a dimer of DNAb helicase (PDB 2r6e).