10/8/94 This directory contains expanded PDB entries with coordinates for the full biological unit (that is, the functional molecule), for cases where there is exact internal symmetry so that only part of the molecule was in the crystallographic asymmetric unit and in the standard PDB entry. For example, standard PDB entries for hemoglobins contain only one alpha-beta dimer, while the entries here contain the full alpha2, beta2 tetramer. To indicate this difference, the files have names starting with "bio" and ending in ".xyz". For example, file pdb1rop.ent contains only the helix-hairpin monomer, while bio1rop.xyz has the full 4-helix bundle. Header information in the file explains its origin and the symmetry elements used to generate it. We hope that these files will be useful for making teaching examples, and for study of important subunit interactions by those not using crystallographic software. Indeed, they were prompted by requests from users. The User Group greatly appreciates the effort that has been put into generating these files by the PDB staff. These files were generated by Enrique Abola and Mingyu Xu from PDB and by John Rose of the University of Pittsburgh. At present this directory is experimental. It contains many, but not all, of the useful cases (for instance, viruses and PFK will be tackled soon). Please let us know if we have missed a molecule that would be useful to you, or if the header information provided is not sufficient (send an Email message to pdbusrgp@suna.biochem.duke.edu). Also, if these files turn out to be a major help to you, please let us know about it.