The RCSB will continue to accept and distribute coordinates in the mmCIF and PDB formats. The PDB format released by the RCSB will be uniform and will continue to use the four-character PDB identifier.
Internally, the RCSB uses the macromolecular Crystallographic Information File (mmCIF)  format to process data. mmCIF is the IUCr-approved data representation for macromolecular structures. The mmCIF dictionary, a collection of more than 1,600 definitions, provides the basis for the RCSB's integrated data processing and query system.
Structures can be deposited in PDB format and then are converted to an mmCIF format file using software developed by the RCSB.
mmCIF information and resources are available at http://ndbserver.rutgers.edu/mmcif/.
1) P.E. Bourne, H.M. Berman, B. McMahon, K.D. Watenpaugh, J. Westbrook, and P.M.D. Fitzgerald. The Macromolecular Crystallographic Information File (mmCIF). Meth. Enzymol. (1997) 277, 571-590.
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