The full clock cycle corresponds to all protein sequences stored in SWISS-PROT (Bairoch and Apweiler 1996) in the year given. The black areas mark the percentage of proteins for which 3D structure could be predicted (for the entire protein or for fragments) by homology to a protein of known 3D structure (Schneider and Sander 1996). On average the alignments between the SWISS-PROT proteins U for which homology modelling could be applied and its homologue of known structure covered about 70% of the residues of the U's.